Fraction

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https://en.wikipedia.org/wiki/Fraction

A cake with one quarter (one fourth) removed. The remaining three fourths are shown by dotted lines and labeled by the fraction 1/4

A fraction (from Latin: fractus, "broken") represents a part of a whole or, more generally, any number of equal parts. When spoken in everyday English, a fraction describes how many parts of a certain size there are, for example, one-half, eight-fifths, three-quarters. A common, vulgar, or simple fraction (examples: ${\displaystyle \frac{1}{2}}$ and ${\displaystyle \frac{17}{3}}$) consists of an integer numerator, displayed above a line (or before a slash like 1⁄2), and a non-zero integer denominator, displayed below (or after) that line. If these integers are positive, then the numerator represents a number of equal parts, and the denominator indicates how many of those parts make up a unit or a whole. For example, in the fraction 3/4, the numerator 3 indicates that the fraction represents 3 equal parts, and the denominator 4 indicates that 4 parts make up a whole. The picture to the right illustrates 3/4 of a cake.

Other uses for fractions are to represent ratios and division. Thus the fraction 3/4 can also be used to represent the ratio 3:4 (the ratio of the part to the whole), and the division 3 ÷ 4 (three divided by four).

We can also write negative fractions, which represent the opposite of a positive fraction. For example, if 1/2 represents a half-dollar profit, then −1/2 represents a half-dollar loss. Because of the rules of division of signed numbers (which states in part that negative divided by positive is negative), −1/2, −1/2 and 1/−2 all represent the same fraction – negative one-half. And because a negative divided by a negative produces a positive, −1/−2 represents positive one-half.

In mathematics the set of all numbers that can be expressed in the form a/b, where a and b are integers and b is not zero, is called the set of rational numbers and is represented by the symbol Q or ℚ, which stands for quotient. A number is a rational number precisely when it can be written in that form (i.e., as a common fraction). However, the word fraction can also be used to describe mathematical expressions that are not rational numbers. Examples of these usages include algebraic fractions (quotients of algebraic expressions), and expressions that contain irrational numbers, such as $\frac{\sqrt{2}}{2}$ (see square root of 2) and π/4 (see proof that π is irrational).

Vocabulary

See also: Numeral (linguistics) § Fractional numbers, and English numerals § Fractions and decimals

In a fraction, the number of equal parts being described is the numerator (from Latin: numerātor, "counter" or "numberer"), and the type or variety of the parts is the denominator (from Latin: dēnōminātor, "thing that names or designates"). As an example, the fraction 8/5 amounts to eight parts, each of which is of the type named "fifth". In terms of division, the numerator corresponds to the dividend, and the denominator corresponds to the divisor.

Informally, the numerator and denominator may be distinguished by placement alone, but in formal contexts they are usually separated by a fraction bar. The fraction bar may be horizontal (as in 1/3), oblique (as in 2/5), or diagonal (as in 4⁄9). These marks are respectively known as the horizontal bar; the virgule, slash (US), or stroke (UK); and the fraction bar, solidus, or fraction slash. In typography, fractions stacked vertically are also known as "en" or "nut fractions", and diagonal ones as "em" or "mutton fractions", based on whether a fraction with a single-digit numerator and denominator occupies the proportion of a narrow en square, or a wider em square. In traditional typefounding, a piece of type bearing a complete fraction (e.g. 1/2) was known as a "case fraction", while those representing only part of fraction were called "piece fractions".

The denominators of English fractions are generally expressed as ordinal numbers, in the plural if the numerator is not 1. (For example, 2/5 and 3/5 are both read as a number of "fifths".) Exceptions include the denominator 2, which is always read "half" or "halves", the denominator 4, which may be alternatively expressed as "quarter"/"quarters" or as "fourth"/"fourths", and the denominator 100, which may be alternatively expressed as "hundredth"/"hundredths" or "percent".

When the denominator is 1, it may be expressed in terms of "wholes" but is more commonly ignored, with the numerator read out as a whole number. For example, 3/1 may be described as "three wholes", or simply as "three". When the numerator is 1, it may be omitted (as in "a tenth" or "each quarter").

The entire fraction may be expressed as a single composition, in which case it is hyphenated, or as a number of fractions with a numerator of one, in which case they are not. (For example, "two-fifths" is the fraction 2/5 and "two fifths" is the same fraction understood as 2 instances of 1/5.) Fractions should always be hyphenated when used as adjectives. Alternatively, a fraction may be described by reading it out as the numerator "over" the denominator, with the denominator expressed as a cardinal number. (For example, 3/1 may also be expressed as "three over one".) The term "over" is used even in the case of solidus fractions, where the numbers are placed left and right of a slash mark. (For example, 1/2 may be read "one-half", "one half", or "one over two".) Fractions with large denominators that are not powers of ten are often rendered in this fashion (e.g., 1/117 as "one over one hundred seventeen"), while those with denominators divisible by ten are typically read in the normal ordinal fashion (e.g., 6/1000000 as "six-millionths", "six millionths", or "six one-millionths").

Forms of fractions

Simple, common, or vulgar fractions

A simple fraction (also known as a common fraction or vulgar fraction, where vulgar is Latin for "common") is a rational number written as a/b or ${\displaystyle \frac{a}{b}}$, where a and b are both integers. As with other fractions, the denominator (b) cannot be zero. Examples include ${\displaystyle \frac{1}{2}}$, ${\displaystyle -\frac{8}{5}}$, ${\displaystyle \frac{-8}{5}}$, and ${\displaystyle \frac{8}{-5}}$. The term was originally used to distinguish this type of fraction from the sexagesimal fraction used in astronomy.

Common fractions can be positive or negative, and they can be proper or improper (see below). Compound fractions, complex fractions, mixed numerals, and decimals (see below) are not common fractions; though, unless irrational, they can be evaluated to a common fraction.

• A unit fraction is a common fraction with a numerator of 1 (e.g., ${\displaystyle \frac{1}{7}}$). Unit fractions can also be expressed using negative exponents, as in 2⁻¹, which represents 1/2, and 2⁻², which represents 1/(2²) or 1/4.
• A dyadic fraction is a common fraction in which the denominator is a power of two, e.g. ${\displaystyle \frac{1}{8}=\frac{1}{2^3}}$.

In Unicode, precomposed fraction characters are in the Number Forms block.

Proper and improper fractions

Common fractions can be classified as either proper or improper. When the numerator and the denominator are both positive, the fraction is called proper if the numerator is less than the denominator, and improper otherwise. The concept of an "improper fraction" is a late development, with the terminology deriving from the fact that "fraction" means "a piece", so a proper fraction must be less than 1. This was explained in the 17th century textbook The Ground of Arts.

In general, a common fraction is said to be a proper fraction, if the absolute value of the fraction is strictly less than one—that is, if the fraction is greater than −1 and less than 1. It is said to be an improper fraction, or sometimes top-heavy fraction, if the absolute value of the fraction is greater than or equal to 1. Examples of proper fractions are 2/3, −3/4, and 4/9, whereas examples of improper fractions are 9/4, −4/3, and 3/3.

Reciprocals and the "invisible denominator"

The reciprocal of a fraction is another fraction with the numerator and denominator exchanged. The reciprocal of ${\displaystyle \frac{3}{7}}$, for instance, is ${\displaystyle \frac{7}{3}}$. The product of a fraction and its reciprocal is 1, hence the reciprocal is the multiplicative inverse of a fraction. The reciprocal of a proper fraction is improper, and the reciprocal of an improper fraction not equal to 1 (that is, numerator and denominator are not equal) is a proper fraction.

When the numerator and denominator of a fraction are equal (for example, ${\displaystyle \frac{7}{7}}$), its value is 1, and the fraction therefore is improper. Its reciprocal is identical and hence also equal to 1 and improper.

Any integer can be written as a fraction with the number one as denominator. For example, 17 can be written as ${\displaystyle \frac{17}{1}}$, where 1 is sometimes referred to as the invisible denominator. Therefore, every fraction or integer, except for zero, has a reciprocal. For example. the reciprocal of 17 is ${\displaystyle \frac{1}{17}}$.

Ratios

A ratio is a relationship between two or more numbers that can be sometimes expressed as a fraction. Typically, a number of items are grouped and compared in a ratio, specifying numerically the relationship between each group. Ratios are expressed as "group 1 to group 2 ... to group n". For example, if a car lot had 12 vehicles, of which

• 2 are white,
• 6 are red, and
• 4 are yellow,

then the ratio of red to white to yellow cars is 6 to 2 to 4. The ratio of yellow cars to white cars is 4 to 2 and may be expressed as 4:2 or 2:1.

A ratio is often converted to a fraction when it is expressed as a ratio to the whole. In the above example, the ratio of yellow cars to all the cars on the lot is 4:12 or 1:3. We can convert these ratios to a fraction, and say that 4/12 of the cars or 1/3 of the cars in the lot are yellow. Therefore, if a person randomly chose one car on the lot, then there is a one in three chance or probability that it would be yellow.

Decimal fractions and percentages

A decimal fraction is a fraction whose denominator is not given explicitly, but is understood to be an integer power of ten. Decimal fractions are commonly expressed using decimal notation in which the implied denominator is determined by the number of digits to the right of a decimal separator, the appearance of which (e.g., a period, an interpunct (·), a comma) depends on the locale (for examples, see decimal separator). Thus, for 0.75 the numerator is 75 and the implied denominator is 10 to the second power, namely, 100, because there are two digits to the right of the decimal separator. In decimal numbers greater than 1 (such as 3.75), the fractional part of the number is expressed by the digits to the right of the decimal (with a value of 0.75 in this case). 3.75 can be written either as an improper fraction, 375/100, or as a mixed number, ${\displaystyle 3\frac{75}{100}}$.

Decimal fractions can also be expressed using scientific notation with negative exponents, such as 6.023×10⁻⁷, which represents 0.0000006023. The 10⁻⁷ represents a denominator of 10⁷. Dividing by 10⁷ moves the decimal point 7 places to the left.

Decimal fractions with infinitely many digits to the right of the decimal separator represent an infinite series. For example, 1/3 = 0.333... represents the infinite series 3/10 + 3/100 + 3/1000 + ....

Another kind of fraction is the percentage (from Latin: per centum, meaning "per hundred", represented by the symbol %), in which the implied denominator is always 100. Thus, 51% means 51/100. Percentages greater than 100 or less than zero are treated in the same way, e.g. 311% equals 311/100, and −27% equals −27/100.

The related concept of permille or parts per thousand (ppt) has an implied denominator of 1000, while the more general parts-per notation, as in 75 parts per million (ppm), means that the proportion is 75/1,000,000.

Whether common fractions or decimal fractions are used is often a matter of taste and context. Common fractions are used most often when the denominator is relatively small. By mental calculation, it is easier to multiply 16 by 3/16 than to do the same calculation using the fraction's decimal equivalent (0.1875). And it is more accurate to multiply 15 by 1/3, for example, than it is to multiply 15 by any decimal approximation of one third. Monetary values are commonly expressed as decimal fractions with denominator 100, i.e., with two decimals, for example $3.75. However, as noted above, in pre-decimal British currency, shillings and pence were often given the form (but not the meaning) of a fraction, as, for example, "3/6" (read "three and six") meaning 3 shillings and 6 pence, and having no relationship to the fraction 3/6.

Mixed numbers

A mixed numeral (also called a mixed fraction or mixed number) is a traditional denotation of the sum of a non-zero integer and a proper fraction (having the same sign). It is used primarily in measurement: ${\displaystyle 2\frac{3}{16}}$inches, for example. Scientific measurements almost invariably use decimal notation rather than mixed numbers. The sum can be implied without the use of a visible operator such as the appropriate "+". For example, in referring to two entire cakes and three quarters of another cake, the numerals denoting the integer part and the fractional part of the cakes can be written next to each other as ${\displaystyle 2\frac{3}{4}}$instead of the unambiguous notation ${\displaystyle 2+\frac{3}{4}.}$ Negative mixed numerals, as in ${\displaystyle -2\frac{3}{4}}$, are treated like ${\displaystyle -\left(2+\frac{3}{4}\right).}$ Any such sum of a whole plus a part can be converted to an improper fraction by applying the rules of adding unlike quantities.

This tradition is, formally, in conflict with the notation in algebra where adjacent symbols, without an explicit infix operator, denote a product. In the expression ${\displaystyle 2x}$, the "understood" operation is multiplication. If x is replaced by, for example, the fraction ${\displaystyle \frac{3}{4}}$, the "understood" multiplication needs to be replaced by explicit multiplication, to avoid the appearance of a mixed number.

When multiplication is intended, ${\displaystyle 2\frac{b}{c}}$ may be written as

${\displaystyle 2\cdot \frac{b}{c},}$ or ${\displaystyle 2\times \frac{b}{c},}$ or ${\displaystyle 2\left(\frac{b}{c}\right),\dots }$

An improper fraction can be converted to a mixed number as follows:

1. Using Euclidean division (division with remainder), divide the numerator by the denominator. In the example, ${\displaystyle \frac{11}{4}}$, divide 11 by 4. 11 ÷ 4 = 2 remainder 3.
2. The quotient (without the remainder) becomes the whole number part of the mixed number. The remainder becomes the numerator of the fractional part. In the example, 2 is the whole number part and 3 is the numerator of the fractional part.
3. The new denominator is the same as the denominator of the improper fraction. In the example, it is 4. Thus, ${\displaystyle \frac{11}{4}=2\frac{3}{4}}$.

Historical notions

Egyptian fraction

An Egyptian fraction is the sum of distinct positive unit fractions, for example ${\displaystyle \frac{1}{2}+\frac{1}{3}}$. This definition derives from the fact that the ancient Egyptians expressed all fractions except ${\displaystyle \frac{1}{2}}$, ${\displaystyle \frac{2}{3}}$ and ${\displaystyle \frac{3}{4}}$ in this manner. Every positive rational number can be expanded as an Egyptian fraction. For example, ${\displaystyle \frac{5}{7}}$ can be written as ${\displaystyle \frac{1}{2}+\frac{1}{6}+\frac{1}{21}.}$ Any positive rational number can be written as a sum of unit fractions in infinitely many ways. Two ways to write ${\displaystyle \frac{13}{17}}$ are ${\displaystyle \frac{1}{2}+\frac{1}{4}+\frac{1}{68}}$ and ${\displaystyle \frac{1}{3}+\frac{1}{4}+\frac{1}{6}+\frac{1}{68}}$.

Complex and compound fractions

Not to be confused with Complex numbers.

In a complex fraction, either the numerator, or the denominator, or both, is a fraction or a mixed number, corresponding to division of fractions. For example, ${\displaystyle \frac{\frac{1}{2}}{\frac{1}{3}}}$ and ${\displaystyle \frac{12\frac{3}{4}}{26}}$ are complex fractions. To reduce a complex fraction to a simple fraction, treat the longest fraction line as representing division. For example:

${\displaystyle \frac{\frac{1}{2}}{\frac{1}{3}}=\frac{1}{2}\times \frac{3}{1}=\frac{3}{2}}$

${\displaystyle \frac{12\frac{3}{4}}{26}=12\frac{3}{4}\cdot \frac{1}{26}=\frac{12\cdot 4+3}{4}\cdot \frac{1}{26}=\frac{51}{4}\cdot \frac{1}{26}=\frac{51}{104}}$

${\displaystyle \frac{\frac{3}{2}}{5}=\frac{3}{2}\times \frac{1}{5}=\frac{3}{10}}$

${\displaystyle \frac{8}{\frac{1}{3}}=8\times \frac{3}{1}=24.}$

If, in a complex fraction, there is no unique way to tell which fraction lines takes precedence, then this expression is improperly formed, because of ambiguity. So 5/10/20/40 is not a valid mathematical expression, because of multiple possible interpretations, e.g. as

${\displaystyle 5/(10/(20/40))=\frac{5}{10/\frac{20}{40}}=\frac{1}{4}}$ or as ${\displaystyle (5/10)/(20/40)=\frac{\frac{5}{10}}{\frac{20}{40}}=1}$

A compound fraction is a fraction of a fraction, or any number of fractions connected with the word of, corresponding to multiplication of fractions. To reduce a compound fraction to a simple fraction, just carry out the multiplication (see the section on multiplication). For example, ${\displaystyle \frac{3}{4}}$ of ${\displaystyle \frac{5}{7}}$ is a compound fraction, corresponding to ${\displaystyle \frac{3}{4}\times \frac{5}{7}=\frac{15}{28}}$. The terms compound fraction and complex fraction are closely related and sometimes one is used as a synonym for the other. (For example, the compound fraction ${\displaystyle \frac{3}{4}\times \frac{5}{7}}$ is equivalent to the complex fraction ${\displaystyle \frac{3/4}{7/5}}$.)

Nevertheless, "complex fraction" and "compound fraction" may both be considered outdated and now used in no well-defined manner, partly even taken synonymously for each other or for mixed numerals. They have lost their meaning as technical terms and the attributes "complex" and "compound" tend to be used in their every day meaning of "consisting of parts".

Arithmetic with fractions

Like whole numbers, fractions obey the commutative, associative, and distributive laws, and the rule against division by zero.

Equivalent fractions

Multiplying the numerator and denominator of a fraction by the same (non-zero) number results in a fraction that is equivalent to the original fraction. This is true because for any non-zero number ${\displaystyle n}$, the fraction ${\displaystyle \frac{n}{n}}$ equals ${\displaystyle 1}$. Therefore, multiplying by ${\displaystyle \frac{n}{n}}$ is the same as multiplying by one, and any number multiplied by one has the same value as the original number. By way of an example, start with the fraction ${\displaystyle \frac{1}{2}}$. When the numerator and denominator are both multiplied by 2, the result is ${\displaystyle \frac{2}{4}}$, which has the same value (0.5) as ${\displaystyle \frac{1}{2}}$. To picture this visually, imagine cutting a cake into four pieces; two of the pieces together (${\displaystyle \frac{2}{4}}$) make up half the cake (${\displaystyle \frac{1}{2}}$).

Simplifying (reducing) fractions

Dividing the numerator and denominator of a fraction by the same non-zero number yields an equivalent fraction: if the numerator and the denominator of a fraction are both divisible by a number (called a factor) greater than 1, then the fraction can be reduced to an equivalent fraction with a smaller numerator and a smaller denominator. For example, if both the numerator and the denominator of the fraction ${\displaystyle \frac{a}{b}}$ are divisible by ${\displaystyle c,}$ then they can be written as ${\displaystyle a=cd}$ and ${\displaystyle b=ce,}$ and the fraction becomes ${\displaystyle \frac{cd}{ce}}$, which can be reduced by dividing both the numerator and denominator by ${\displaystyle c}$ to give the reduced fraction ${\displaystyle \frac{d}{e}.}$

If one takes for c the greatest common divisor of the numerator and the denominator, one gets the equivalent fraction whose numerator and denominator have the lowest absolute values. One says that the fraction has been reduced to its lowest terms.

If the numerator and the denominator do not share any factor greater than 1, the fraction is already reduced to its lowest terms, and it is said to be irreducible, reduced, or in simplest terms. For example, ${\displaystyle \frac{3}{9}}$ is not in lowest terms because both 3 and 9 can be exactly divided by 3. In contrast, ${\displaystyle \frac{3}{8}}$ is in lowest terms—the only positive integer that goes into both 3 and 8 evenly is 1.

Using these rules, we can show that ${\displaystyle \frac{5}{10}=\frac{1}{2}=\frac{10}{20}=\frac{50}{100}}$, for example.

As another example, since the greatest common divisor of 63 and 462 is 21, the fraction ${\displaystyle \frac{63}{462}}$ can be reduced to lowest terms by dividing the numerator and denominator by 21:

${\displaystyle \frac{63}{462}=\frac{63÷21}{462÷21}=\frac{3}{22}}$

The Euclidean algorithm gives a method for finding the greatest common divisor of any two integers.

Comparing fractions

Comparing fractions with the same positive denominator yields the same result as comparing the numerators:

${\displaystyle \frac{3}{4}>\frac{2}{4}}$ because 3 > 2, and the equal denominators ${\displaystyle 4}$ are positive.

If the equal denominators are negative, then the opposite result of comparing the numerators holds for the fractions:

${\displaystyle \frac{3}{-4}<\frac{2}{-4}\text{ because }\frac{a}{-b}=\frac{-a}{b}\text{ and }-3<-2.}$

If two positive fractions have the same numerator, then the fraction with the smaller denominator is the larger number. When a whole is divided into equal pieces, if fewer equal pieces are needed to make up the whole, then each piece must be larger. When two positive fractions have the same numerator, they represent the same number of parts, but in the fraction with the smaller denominator, the parts are larger.

One way to compare fractions with different numerators and denominators is to find a common denominator. To compare ${\displaystyle \frac{a}{b}}$ and ${\displaystyle \frac{c}{d}}$, these are converted to ${\displaystyle \frac{a\cdot d}{b\cdot d}}$ and ${\displaystyle \frac{b\cdot c}{b\cdot d}}$ (where the dot signifies multiplication and is an alternative symbol to ×). Then bd is a common denominator and the numerators ad and bc can be compared. It is not necessary to determine the value of the common denominator to compare fractions – one can just compare ad and bc, without evaluating bd, e.g., comparing ${\displaystyle \frac{2}{3}}$ ? ${\displaystyle \frac{1}{2}}$ gives ${\displaystyle \frac{4}{6}>\frac{3}{6}}$.

For the more laborious question ${\displaystyle \frac{5}{18}}$ ? ${\displaystyle \frac{4}{17},}$ multiply top and bottom of each fraction by the denominator of the other fraction, to get a common denominator, yielding ${\displaystyle \frac{5\times 17}{18\times 17}}$ ? ${\displaystyle \frac{18\times 4}{18\times 17}}$. It is not necessary to calculate ${\displaystyle 18\times 17}$ – only the numerators need to be compared. Since 5×17 (= 85) is greater than 4×18 (= 72), the result of comparing is ${\displaystyle \frac{5}{18}>\frac{4}{17}}$.

Because every negative number, including negative fractions, is less than zero, and every positive number, including positive fractions, is greater than zero, it follows that any negative fraction is less than any positive fraction. This allows, together with the above rules, to compare all possible fractions.

Addition

The first rule of addition is that only like quantities can be added; for example, various quantities of quarters. Unlike quantities, such as adding thirds to quarters, must first be converted to like quantities as described below: Imagine a pocket containing two quarters, and another pocket containing three quarters; in total, there are five quarters. Since four quarters is equivalent to one (dollar), this can be represented as follows:

${\displaystyle \frac{2}{4}+\frac{3}{4}=\frac{5}{4}=1\frac{1}{4}}$.

If ${\displaystyle \frac{1}{2}}$ of a cake is to be added to ${\displaystyle \frac{1}{4}}$ of a cake, the pieces need to be converted into comparable quantities, such as cake-eighths or cake-quarters.

Adding unlike quantities

To add fractions containing unlike quantities (e.g. quarters and thirds), it is necessary to convert all amounts to like quantities. It is easy to work out the chosen type of fraction to convert to; simply multiply together the two denominators (bottom number) of each fraction. In case of an integer number apply the invisible denominator ${\displaystyle 1.}$

For adding quarters to thirds, both types of fraction are converted to twelfths, thus:

${\displaystyle \frac{1}{4}+\frac{1}{3}=\frac{1\times 3}{4\times 3}+\frac{1\times 4}{3\times 4}=\frac{3}{12}+\frac{4}{12}=\frac{7}{12}.}$

Consider adding the following two quantities:

${\displaystyle \frac{3}{5}+\frac{2}{3}}$

First, convert ${\displaystyle \frac{3}{5}}$ into fifteenths by multiplying both the numerator and denominator by three: ${\displaystyle \frac{3}{5}\times \frac{3}{3}=\frac{9}{15}}$. Since ${\displaystyle \frac{3}{3}}$ equals 1, multiplication by ${\displaystyle \frac{3}{3}}$ does not change the value of the fraction.

Second, convert ${\displaystyle \frac{2}{3}}$ into fifteenths by multiplying both the numerator and denominator by five: ${\displaystyle \frac{2}{3}\times \frac{5}{5}=\frac{10}{15}}$.

Now it can be seen that:

${\displaystyle \frac{3}{5}+\frac{2}{3}}$

is equivalent to:

${\displaystyle \frac{9}{15}+\frac{10}{15}=\frac{19}{15}=1\frac{4}{15}}$

This method can be expressed algebraically:

${\displaystyle \frac{a}{b}+\frac{c}{d}=\frac{ad+cb}{bd}}$

This algebraic method always works, thereby guaranteeing that the sum of simple fractions is always again a simple fraction. However, if the single denominators contain a common factor, a smaller denominator than the product of these can be used. For example, when adding ${\displaystyle \frac{3}{4}}$ and ${\displaystyle \frac{5}{6}}$ the single denominators have a common factor ${\displaystyle 2,}$ and therefore, instead of the denominator 24 (4 × 6), the halved denominator 12 may be used, not only reducing the denominator in the result, but also the factors in the numerator.

${\displaystyle \begin{array}{rlr}\frac{3}{4}+\frac{5}{6}& =\frac{3\cdot 6}{4\cdot 6}+\frac{4\cdot 5}{4\cdot 6}=\frac{18}{24}+\frac{20}{24}& =\frac{19}{12}\\ & =\frac{3\cdot 3}{4\cdot 3}+\frac{2\cdot 5}{2\cdot 6}=\frac{9}{12}+\frac{10}{12}& =\frac{19}{12}\end{array}}$

The smallest possible denominator is given by the least common multiple of the single denominators, which results from dividing the rote multiple by all common factors of the single denominators. This is called the least common denominator.

Subtraction

The process for subtracting fractions is, in essence, the same as that of adding them: find a common denominator, and change each fraction to an equivalent fraction with the chosen common denominator. The resulting fraction will have that denominator, and its numerator will be the result of subtracting the numerators of the original fractions. For instance,

${\displaystyle \frac{2}{3}-\frac{1}{2}=\frac{4}{6}-\frac{3}{6}=\frac{1}{6}}$

Multiplication

Multiplying a fraction by another fraction

To multiply fractions, multiply the numerators and multiply the denominators. Thus:

${\displaystyle \frac{2}{3}\times \frac{3}{4}=\frac{6}{12}}$

To explain the process, consider one third of one quarter. Using the example of a cake, if three small slices of equal size make up a quarter, and four quarters make up a whole, twelve of these small, equal slices make up a whole. Therefore, a third of a quarter is a twelfth. Now consider the numerators. The first fraction, two thirds, is twice as large as one third. Since one third of a quarter is one twelfth, two thirds of a quarter is two twelfth. The second fraction, three quarters, is three times as large as one quarter, so two thirds of three quarters is three times as large as two thirds of one quarter. Thus two thirds times three quarters is six twelfths.

A short cut for multiplying fractions is called "cancellation". Effectively the answer is reduced to lowest terms during multiplication. For example:

${\displaystyle \frac{2}{3}\times \frac{3}{4}=\frac{{\cancel{2}}^1}{{\cancel{3}}^1}\times \frac{{\cancel{3}}^1}{{\cancel{4}}^2}=\frac{1}{1}\times \frac{1}{2}=\frac{1}{2}}$

A two is a common factor in both the numerator of the left fraction and the denominator of the right and is divided out of both. Three is a common factor of the left denominator and right numerator and is divided out of both.

Multiplying a fraction by a whole number

Since a whole number can be rewritten as itself divided by 1, normal fraction multiplication rules can still apply.

${\displaystyle 6\times \frac{3}{4}=\frac{6}{1}\times \frac{3}{4}=\frac{18}{4}}$

This method works because the fraction 6/1 means six equal parts, each one of which is a whole.

Multiplying mixed numbers

When multiplying mixed numbers, it is considered preferable to convert the mixed number into an improper fraction. For example:

${\displaystyle 3\times 2\frac{3}{4}=3\times \left(\frac{8}{4}+\frac{3}{4}\right)=3\times \frac{11}{4}=\frac{33}{4}=8\frac{1}{4}}$

In other words, ${\displaystyle 2\frac{3}{4}}$ is the same as ${\displaystyle \frac{8}{4}+\frac{3}{4}}$, making 11 quarters in total (because 2 cakes, each split into quarters makes 8 quarters total) and 33 quarters is ${\displaystyle 8\frac{1}{4}}$, since 8 cakes, each made of quarters, is 32 quarters in total.

Division

To divide a fraction by a whole number, you may either divide the numerator by the number, if it goes evenly into the numerator, or multiply the denominator by the number. For example, ${\displaystyle \frac{10}{3}÷5}$ equals ${\displaystyle \frac{2}{3}}$ and also equals ${\displaystyle \frac{10}{3\cdot 5}=\frac{10}{15}}$, which reduces to ${\displaystyle \frac{2}{3}}$. To divide a number by a fraction, multiply that number by the reciprocal of that fraction. Thus, ${\displaystyle \frac{1}{2}÷\frac{3}{4}=\frac{1}{2}\times \frac{4}{3}=\frac{1\cdot 4}{2\cdot 3}=\frac{2}{3}}$.

Converting between decimals and fractions

To change a common fraction to a decimal, do a long division of the decimal representations of the numerator by the denominator (this is idiomatically also phrased as "divide the denominator into the numerator"), and round the answer to the desired accuracy. For example, to change 1/4 to a decimal, divide 1.00 by 4 ("4 into 1.00"), to obtain 0.25. To change 1/3 to a decimal, divide 1.000... by 3 ("3 into 1.000..."), and stop when the desired accuracy is obtained, e.g., at 4 decimals with 0.3333. The fraction 1/4 can be written exactly with two decimal digits, while the fraction 1/3 cannot be written exactly as a decimal with a finite number of digits. To change a decimal to a fraction, write in the denominator a 1 followed by as many zeroes as there are digits to the right of the decimal point, and write in the numerator all the digits of the original decimal, just omitting the decimal point. Thus ${\displaystyle 12.3456=\frac{123456}{10000}.}$

Converting repeating decimals to fractions

Further information: Decimal representation § Conversion to fraction

See also: Repeating decimal

Decimal numbers, while arguably more useful to work with when performing calculations, sometimes lack the precision that common fractions have. Sometimes an infinite repeating decimal is required to reach the same precision. Thus, it is often useful to convert repeating decimals into fractions.

A conventional way to indicate a repeating decimal is to place a bar (known as a vinculum) over the digits that repeat, for example 0.789 = 0.789789789... For repeating patterns that begin immediately after the decimal point, the result of the conversion is the fraction with the pattern as a numerator, and the same number of nines as a denominator. For example:

0.5 = 5/9

0.62 = 62/99

0.264 = 264/999

0.6291 = 6291/9999

If leading zeros precede the pattern, the nines are suffixed by the same number of trailing zeros:

0.05 = 5/90

0.000392 = 392/999000

0.0012 = 12/9900

If a non-repeating set of decimals precede the pattern (such as 0.1523987), one may write the number as the sum of the non-repeating and repeating parts, respectively:

0.1523 + 0.0000987

Then, convert both parts to fractions, and add them using the methods described above:

1523 / 10000 + 987 / 9990000 = 1522464 / 9990000

Alternatively, algebra can be used, such as below:

1. Let x = the repeating decimal:

   x = 0.1523987

2. Multiply both sides by the power of 10 just great enough (in this case 10⁴) to move the decimal point just before the repeating part of the decimal number:

   10,000x = 1,523.987

3. Multiply both sides by the power of 10 (in this case 10³) that is the same as the number of places that repeat:

   10,000,000x = 1,523,987.987

4. Subtract the two equations from each other (if a = b and c = d, then a − c = b − d):

   10,000,000x − 10,000x = 1,523,987.987 − 1,523.987

5. Continue the subtraction operation to clear the repeating decimal:

   9,990,000x = 1,523,987 − 1,523

   = 1,522,464

6. Divide both sides by 9,990,000 to represent x as a fraction

   x = 1522464/9990000

Fractions in abstract mathematics

In addition to being of great practical importance, fractions are also studied by mathematicians, who check that the rules for fractions given above are consistent and reliable. Mathematicians define a fraction as an ordered pair ${\displaystyle (a,b)}$ of integers ${\displaystyle a}$ and ${\displaystyle b\ne 0,}$ for which the operations addition, subtraction, multiplication, and division are defined as follows:

${\displaystyle (a,b)+(c,d)=(ad+bc,bd)}$

${\displaystyle (a,b)-(c,d)=(ad-bc,bd)}$

${\displaystyle (a,b)\cdot (c,d)=(ac,bd)}$

${\displaystyle (a,b)÷(c,d)=(ad,bc)(\text{with, additionally, }c\ne 0)}$

These definitions agree in every case with the definitions given above; only the notation is different. Alternatively, instead of defining subtraction and division as operations, the "inverse" fractions with respect to addition and multiplication might be defined as:

${\displaystyle \begin{array}{rlrl}-(a,b)& =(-a,b)& & \text{additive inverse fractions,}\\ & & & \text{with }(0,b)\text{ as additive unities, and}\\ (a,b{)}^{-1}& =(b,a)& & \text{multiplicative inverse fractions, for }a\ne 0,\\ & & & \text{with }(b,b)\text{ as multiplicative unities}.\end{array}}$

Furthermore, the relation, specified as

${\displaystyle (a,b)\sim (c,d)⟺ad=bc,}$

is an equivalence relation of fractions. Each fraction from one equivalence class may be considered as a representative for the whole class, and each whole class may be considered as one abstract fraction. This equivalence is preserved by the above defined operations, i.e., the results of operating on fractions are independent of the selection of representatives from their equivalence class. Formally, for addition of fractions

${\displaystyle (a,b)\sim (a^{\prime },b^{\prime })}$ and ${\displaystyle (c,d)\sim (c^{\prime },d^{\prime })}$ imply

${\displaystyle ((a,b)+(c,d))\sim ((a^{\prime },b^{\prime })+(c^{\prime },d^{\prime }))}$

and similarly for the other operations.

In the case of fractions of integers, the fractions a/b with a and b coprime and b > 0 are often taken as uniquely determined representatives for their equivalent fractions, which are considered to be the same rational number. This way the fractions of integers make up the field of the rational numbers.

More generally, a and b may be elements of any integral domain R, in which case a fraction is an element of the field of fractions of R. For example, polynomials in one indeterminate, with coefficients from some integral domain D, are themselves an integral domain, call it P. So for a and b elements of P, the generated field of fractions is the field of rational fractions (also known as the field of rational functions).

Algebraic fractions

Main article: Algebraic fraction

An algebraic fraction is the indicated quotient of two algebraic expressions. As with fractions of integers, the denominator of an algebraic fraction cannot be zero. Two examples of algebraic fractions are ${\displaystyle \frac{3x}{x^2+2x-3}}$ and ${\displaystyle \frac{\sqrt{x+2}}{x^2-3}}$. Algebraic fractions are subject to the same field properties as arithmetic fractions.

If the numerator and the denominator are polynomials, as in ${\displaystyle \frac{3x}{x^2+2x-3}}$, the algebraic fraction is called a rational fraction (or rational expression). An irrational fraction is one that is not rational, as, for example, one that contains the variable under a fractional exponent or root, as in ${\displaystyle \frac{\sqrt{x+2}}{x^2-3}}$.

The terminology used to describe algebraic fractions is similar to that used for ordinary fractions. For example, an algebraic fraction is in lowest terms if the only factors common to the numerator and the denominator are 1 and −1. An algebraic fraction whose numerator or denominator, or both, contain a fraction, such as ${\displaystyle \frac{1+\frac{1}{x}}{1-\frac{1}{x}}}$, is called a complex fraction.

The field of rational numbers is the field of fractions of the integers, while the integers themselves are not a field but rather an integral domain. Similarly, the rational fractions with coefficients in a field form the field of fractions of polynomials with coefficient in that field. Considering the rational fractions with real coefficients, radical expressions representing numbers, such as ${\displaystyle \sqrt{2}/2,}$ are also rational fractions, as are a transcendental numbers such as $\pi /2,$ since all of ${\displaystyle \sqrt{2},\pi ,}$ and ${\displaystyle 2}$ are real numbers, and thus considered as coefficients. These same numbers, however, are not rational fractions with integer coefficients.

The term partial fraction is used when decomposing rational fractions into sums of simpler fractions. For example, the rational fraction ${\displaystyle \frac{2x}{x^2-1}}$ can be decomposed as the sum of two fractions: ${\displaystyle \frac{1}{x+1}+\frac{1}{x-1}.}$ This is useful for the computation of antiderivatives of rational functions (see partial fraction decomposition for more).

Radical expressions

Main articles: Nth root and Rationalization (mathematics)

A fraction may also contain radicals in the numerator or the denominator. If the denominator contains radicals, it can be helpful to rationalize it (compare Simplified form of a radical expression), especially if further operations, such as adding or comparing that fraction to another, are to be carried out. It is also more convenient if division is to be done manually. When the denominator is a monomial square root, it can be rationalized by multiplying both the top and the bottom of the fraction by the denominator:

${\displaystyle \frac{3}{\sqrt{7}}=\frac{3}{\sqrt{7}}\cdot \frac{\sqrt{7}}{\sqrt{7}}=\frac{3\sqrt{7}}{7}}$

The process of rationalization of binomial denominators involves multiplying the top and the bottom of a fraction by the conjugate of the denominator so that the denominator becomes a rational number. For example:

${\displaystyle \frac{3}{3-2\sqrt{5}}=\frac{3}{3-2\sqrt{5}}\cdot \frac{3+2\sqrt{5}}{3+2\sqrt{5}}=\frac{3(3+2\sqrt{5})}{3^2-(2\sqrt{5}{)}^2}=\frac{3(3+2\sqrt{5})}{9-20}=-\frac{9+6\sqrt{5}}{11}}$

${\displaystyle \frac{3}{3+2\sqrt{5}}=\frac{3}{3+2\sqrt{5}}\cdot \frac{3-2\sqrt{5}}{3-2\sqrt{5}}=\frac{3(3-2\sqrt{5})}{3^2-(2\sqrt{5}{)}^2}=\frac{3(3-2\sqrt{5})}{9-20}=-\frac{9-6\sqrt{5}}{11}}$

Even if this process results in the numerator being irrational, like in the examples above, the process may still facilitate subsequent manipulations by reducing the number of irrationals one has to work with in the denominator.

Typographical variations

See also: Slash § Encoding

In computer displays and typography, simple fractions are sometimes printed as a single character, e.g. ½ (one half). See the article on Number Forms for information on doing this in Unicode.

Scientific publishing distinguishes four ways to set fractions, together with guidelines on use:

• Special fractions: fractions that are presented as a single character with a slanted bar, with roughly the same height and width as other characters in the text. Generally used for simple fractions, such as: ½, ⅓, ⅔, ¼, and ¾. Since the numerals are smaller, legibility can be an issue, especially for small-sized fonts. These are not used in modern mathematical notation, but in other contexts.
• Case fractions: similar to special fractions, these are rendered as a single typographical character, but with a horizontal bar, thus making them upright. An example would be ${\displaystyle \frac{1}{2}}$, but rendered with the same height as other characters. Some sources include all rendering of fractions as case fractions if they take only one typographical space, regardless of the direction of the bar.
• Shilling or solidus fractions: 1/2, so called because this notation was used for pre-decimal British currency (£sd), as in "2/6" for a half crown, meaning two shillings and six pence. While the notation "two shillings and six pence" did not represent a fraction, the forward slash is now used in fractions, especially for fractions inline with prose (rather than displayed), to avoid uneven lines. It is also used for fractions within fractions (complex fractions) or within exponents to increase legibility. Fractions written this way, also known as piece fractions, are written all on one typographical line, but take 3 or more typographical spaces.
• Built-up fractions: ${\displaystyle \frac{1}{2}}$. This notation uses two or more lines of ordinary text and results in a variation in spacing between lines when included within other text. While large and legible, these can be disruptive, particularly for simple fractions or within complex fractions.

History

The earliest fractions were reciprocals of integers: ancient symbols representing one part of two, one part of three, one part of four, and so on. The Egyptians used Egyptian fractions c. 1000 BC. About 4000 years ago, Egyptians divided with fractions using slightly different methods. They used least common multiples with unit fractions. Their methods gave the same answer as modern methods. The Egyptians also had a different notation for dyadic fractions in the Akhmim Wooden Tablet and several Rhind Mathematical Papyrus problems.

The Greeks used unit fractions and (later) continued fractions. Followers of the Greek philosopher Pythagoras (c. 530 BC) discovered that the square root of two cannot be expressed as a fraction of integers. (This is commonly though probably erroneously ascribed to Hippasus of Metapontum, who is said to have been executed for revealing this fact.) In 150 BC Jain mathematicians in India wrote the "Sthananga Sutra", which contains work on the theory of numbers, arithmetical operations, and operations with fractions.

A modern expression of fractions known as bhinnarasi seems to have originated in India in the work of Aryabhatta (c. AD 500), Brahmagupta (c. 628), and Bhaskara (c. 1150). Their works form fractions by placing the numerators (Sanskrit: amsa) over the denominators (cheda), but without a bar between them. In Sanskrit literature, fractions were always expressed as an addition to or subtraction from an integer. The integer was written on one line and the fraction in its two parts on the next line. If the fraction was marked by a small circle ⟨०⟩ or cross ⟨+⟩, it is subtracted from the integer; if no such sign appears, it is understood to be added. For example, Bhaskara I writes:

६  १  २

१  १  १_०

४  ५  ९

which is the equivalent of

6  1  2

1  1  −1

4  5  9

and would be written in modern notation as 61/4, 11/5, and 2 − 1/9 (i.e., 18/9).

The horizontal fraction bar is first attested in the work of Al-Hassār (fl. 1200), a Muslim mathematician from Fez, Morocco, who specialized in Islamic inheritance jurisprudence. In his discussion he writes: "for example, if you are told to write three-fifths and a third of a fifth, write thus, ${\displaystyle \frac{31}{53}}$". The same fractional notation—with the fraction given before the integer—appears soon after in the work of Leonardo Fibonacci in the 13th century.

In discussing the origins of decimal fractions, Dirk Jan Struik states:

The introduction of decimal fractions as a common computational practice can be dated back to the Flemish pamphlet De Thiende, published at Leyden in 1585, together with a French translation, La Disme, by the Flemish mathematician Simon Stevin (1548–1620), then settled in the Northern Netherlands. It is true that decimal fractions were used by the Chinese many centuries before Stevin and that the Persian astronomer Al-Kāshī used both decimal and sexagesimal fractions with great ease in his Key to arithmetic (Samarkand, early fifteenth century).

While the Persian mathematician Jamshīd al-Kāshī claimed to have discovered decimal fractions himself in the 15th century, J. Lennart Berggren notes that he was mistaken, as decimal fractions were first used five centuries before him by the Baghdadi mathematician Abu'l-Hasan al-Uqlidisi as early as the 10th century.

In formal education

Pedagogical tools

In primary schools, fractions have been demonstrated through Cuisenaire rods, Fraction Bars, fraction strips, fraction circles, paper (for folding or cutting), pattern blocks, pie-shaped pieces, plastic rectangles, grid paper, dot paper, geoboards, counters and computer software.

Documents for teachers

Several states in the United States have adopted learning trajectories from the Common Core State Standards Initiative's guidelines for mathematics education. Aside from sequencing the learning of fractions and operations with fractions, the document provides the following definition of a fraction: "A number expressible in the form ${\displaystyle a}$/${\displaystyle b}$ where ${\displaystyle a}$ is a whole number and ${\displaystyle b}$ is a positive whole number. (The word fraction in these standards always refers to a non-negative number.)" The document itself also refers to negative fractions.

Assessment of kidney function

From Wikipedia, the free encyclopedia

https://en.wikipedia.org/wiki/Assessment_of_kidney_function 

Diagram showing a schematic nephron and its blood supply. The basic physiologic mechanisms of handling fluid and electrolytes by the nephron - filtration, secretion, reabsorption, and excretion - are labelled.

Assessment of kidney function occurs in different ways, using the presence of symptoms and signs, as well as measurements using urine tests, blood tests, and medical imaging.

Functions of a healthy kidney include maintaining a person's fluid balance, maintaining an acid-base balance; regulating electrolytes including sodium, potassium, and other electrolytes; clearing toxins; regulating blood pressure; and regulating hormones, such as erythropoietin; and activation of vitamin D.

Description

Main article: Renal physiology

The functions of the kidney include maintenance of acid-base balance; regulation of fluid balance; regulation of sodium, potassium, and other electrolytes; clearance of toxins; absorption of glucose, amino acids, and other small molecules; regulation of blood pressure; production of various hormones, such as erythropoietin; and activation of vitamin D.

The GFR is regarded as the best overall measure of the kidney's ability to carry out these numerous functions. An estimate of the GFR is used clinically to determine the degree of kidney impairment and to track the progression of the disease. The GFR, however, does not reveal the source of the kidney disease. This is accomplished by urinalysis, measurement of urine protein excretion, kidney imaging, and, if necessary, kidney biopsy.

Much of renal physiology is studied at the level of the nephron – the smallest functional unit of the kidney. Each nephron begins with a filtration component that filters the blood entering the kidney. This filtrate then flows along the length of the nephron, which is a tubular structure lined by a single layer of specialized cells and surrounded by capillaries. The major functions of these lining cells are the reabsorption of water and small molecules from the filtrate into the blood, and the secretion of wastes from the blood into the urine.

Proper function of the kidney requires that it receives and adequately filters blood. This is performed at the microscopic level by many hundreds of thousands of filtration units called renal corpuscles, each of which is composed of a glomerulus and a Bowman's capsule. A global assessment of renal function is often ascertained by estimating the rate of filtration, called the glomerular filtration rate (GFR).

Clinical assessment

Clinical assessment can be used to assess the function of the kidneys. This is because a person with abnormally functioning kidneys may have symptoms that develop. For example, a person with chronic kidney disease may develop oedema due to failure of the kidneys to regulate water balance. They may develop evidence of chronic kidney disease, that can be used to assess its severity, for example high blood pressure, osteoporosis or anaemia. If the kidneys are unable to excrete urea, a person may develop a widespread itch or confusion.

Urine tests

Part of the assessment of kidney function includes the measurement of urine and its contents. Abnormal kidney function may cause too much or too little urine to be produced. The ability of the kidneys to filter protein is often measured, as urine albumin or urine protein levels, measured either at a single instance or, because of variation throughout the day, as 24-hour urine tests.

Blood tests

Blood tests are also used to assess kidney function. These include tests that are intended to directly measure the function of the kidneys, as well as tests that assess the function of the kidneys by looking for evidence of problems associated with abnormal function. One of the measures of kidney function is the glomerular filtration rate (GFR). Other tests that can assess the function of the kidneys include assessment of electrolyte levels such as potassium and phosphate, assessment of acid-base status by the measurement of bicarbonate levels from a vein, and assessment of the full blood count for anaemia.

Glomerular filtration rate

Main article: Glomerular filtration rate

The glomerular filtration rate (GFR) describes the volume of fluid filtered from the renal (kidney) glomerular capillaries into the Bowman's capsule per unit time. Creatinine clearance is the volume of blood plasma that is cleared of creatinine per unit time and is a useful measure for approximating the GFR. Creatinine clearance exceeds GFR due to creatinine secretion, which can be blocked by cimetidine. Both GFR and C_Cr may be accurately calculated by comparative measurements of substances in the blood and urine, or estimated by formulas using just a blood test result (eGFR and eC_Cr) The results of these tests are used to assess the excretory function of the kidneys. Staging of chronic kidney disease is based on categories of GFR as well as albuminuria and cause of kidney disease.

Central to the physiologic maintenance of GFR is the differential basal tone of the afferent and efferent arterioles (see diagram). In other words, the filtration rate is dependent on the difference between the higher blood pressure created by vasoconstriction of the input or afferent arteriole versus the lower blood pressure created by lesser vasoconstriction of the output or efferent arteriole.

GFR is equal to the renal clearance ratio when any solute is freely filtered and is neither reabsorbed nor secreted by the kidneys. The rate therefore measured is the quantity of the substance in the urine that originated from a calculable volume of blood. Relating this principle to the below equation – for the substance used, the product of urine concentration and urine flow equals the mass of substance excreted during the time that urine has been collected. This mass equals the mass filtered at the glomerulus as nothing is added or removed in the nephron. Dividing this mass by the plasma concentration gives the volume of plasma which the mass must have originally come from, and thus the volume of plasma fluid that has entered Bowman's capsule within the aforementioned period of time. The GFR is typically recorded in units of volume per time, e.g., milliliters per minute (mL/min). Compare to filtration fraction.

${\displaystyle GFR=\frac{\text{Urine Concentration}\times \text{Urine Flow}}{\text{Plasma Concentration}}}$

There are several different techniques used to calculate or estimate the glomerular filtration rate (GFR or eGFR). The above formula only applies for GFR calculation when it is equal to the Clearance Rate.

The normal range of GFR, adjusted for body surface area, is 100–130 average 125 (mL/min)/(1.73 m²) in men and 90–120 (mL/min)/(1.73 m²) in women younger than the age of 40. In children, GFR measured by inulin clearance is 110 (mL/min)/(1.73 m²) until 2 years of age in both sexes, and then it progressively decreases. After age 40, GFR decreases progressively with age, by 0.4–1.2 mL/min per year.

Estimated GFR (eGFR) is now recommended by clinical practice guidelines and regulatory agencies for routine evaluation of GFR whereas measured GFR (mGFR) is recommended as a confirmatory test when more accurate assessment is required.

Medical imaging

The kidney function can also be assessed with medical imaging. Some forms of imaging, such as kidney ultrasound or CT scans, may assess kidney function by indicating chronic disease that can impact function, by showing a small or shrivelled kidney. Other tests, such as nuclear medicine tests, directly assess the function of the kidney by measuring the perfusion and excretion of radioactive substances through the kidneys.

Kidney function in disease

A decreased renal function can be caused by many types of kidney disease. Upon presentation of decreased renal function, it is recommended to perform a history and physical examination, as well as performing a renal ultrasound and a urinalysis. The most relevant items in the history are medications, edema, nocturia, gross hematuria, family history of kidney disease, diabetes and polyuria. The most important items in a physical examination are signs of vasculitis, lupus erythematosus, diabetes, endocarditis and hypertension.

A urinalysis is helpful even when not showing any pathology, as this finding suggests an extrarenal etiology. Proteinuria and/or urinary sediment usually indicates the presence of glomerular disease. Hematuria may be caused by glomerular disease or by a disease along the urinary tract.

The most relevant assessments in a renal ultrasound are renal sizes, echogenicity and any signs of hydronephrosis. Renal enlargement usually indicates diabetic nephropathy, focal segmental glomerular sclerosis or myeloma. Renal atrophy suggests longstanding chronic renal disease.

Chronic kidney disease stages

Main article: Chronic kidney disease

Risk factors for kidney disease include diabetes, high blood pressure, family history, older age, ethnic group and smoking. For most patients, a GFR over 60 (mL/min)/(1.73 m²) is adequate. But significant decline of the GFR from a previous test result can be an early indicator of kidney disease requiring medical intervention. The sooner kidney dysfunction is diagnosed and treated the greater odds of preserving remaining nephrons, and preventing the need for dialysis.

CKD stage	GFR level ((mL/min)/(1.73 m2))
Stage 1	≥ 90
Stage 2	60–89
Stage 3	30–59
Stage 4	15–29
Stage 5	< 15

The severity of chronic kidney disease (CKD) is described by six stages; the most severe three are defined by the MDRD-eGFR value, and first three also depend on whether there is other evidence of kidney disease (e.g., proteinuria):

0) Normal kidney function – GFR above 90 (mL/min)/(1.73 m²) and no proteinuria

1) CKD1 – GFR above 90 (mL/min)/(1.73 m²) with evidence of kidney damage

2) CKD2 (mild) – GFR of 60 to 89 (mL/min)/(1.73 m²) with evidence of kidney damage

3) CKD3 (moderate) – GFR of 30 to 59 (mL/min)/(1.73 m²)

4) CKD4 (severe) – GFR of 15 to 29 (mL/min)/(1.73 m²)

5) CKD5 kidney failure – GFR less than 15 (mL/min)/(1.73 m²) Some people add CKD5D for those stage 5 patients requiring dialysis; many patients in CKD5 are not yet on dialysis.

Note: others add a "T" to patients who have had a transplant regardless of stage.

Not all clinicians agree with the above classification, suggesting that it may mislabel patients with mildly reduced kidney function, especially the elderly, as having a disease. A conference was held in 2009 regarding these controversies by Kidney Disease: Improving Global Outcomes (KDIGO) on CKD: Definition, Classification and Prognosis, gathering data on CKD prognosis to refine the definition and staging of CKD.

Tumor marker

From Wikipedia, the free encyclopedia
https://en.wikipedia.org/wiki/Tumor_marker

A tumor marker is a biomarker found in blood, urine, or body tissues that can be elevated by the presence of one or more types of cancer. There are many different tumor markers, each indicative of a particular disease process, and they are used in oncology to help detect the presence of cancer. An elevated level of a tumor marker can indicate cancer; however, there can also be other causes of the elevation (false positive values).

Tumor markers can be produced directly by the tumor or by non-tumor cells as a response to the presence of a tumor.

Although mammography, ultrasonography, computed tomography, magnetic resonance imaging scans, and tumor marker assays help in the staging and treatment of the cancer, they are usually not definitive diagnostic tests. The diagnosis is mostly confirmed by biopsy.

Classification

On the basis of their chemical nature, tumor markers can be proteins, conjugated proteins, peptides and carbohydrates. Proteins or conjugated proteins may be enzymes, hormones or fragments of proteins. Sequencing of genes for diagnostic purposes is mostly classified under the biomarker heading and is not discussed here.

Uses

Tumor markers may be used for the following purposes:

• Screening for common cancers on a population basis. Broad screening for all or most types of cancer was originally suggested, but has since been shown not to be a realistic goal. Screening for specific cancer types or locations requires a level of specificity and sensitivity that has so far only been reached by Example: elevated prostate specific antigen suggests that is used in some countries to screen for prostate cancer.
• Monitoring of cancer survivors after treatment, detection of recurrent disease. Example: elevated AFP in a child previously treated for teratoma suggests relapse with endodermal sinus tumor.
• Diagnosis of specific tumor types, particularly in certain brain tumors and other instances where biopsy is not feasible.
• Confirmation of diagnosis to verify the characteristics such as size and aggressiveness of a tumor and thereby to help in the evaluation of a suitable treatment schedule.
• Staging: some tumor markers are included in the staging procedures for some tumor localizations.
• Prognosis to plan the treatment when used pre-treatment and to help the patient to plan his future when used after the operation of cure.
• To verify the effect of treatment, to change the treatment if ineffective.
• As companion diagnostic to verify if the treatment is suited for the type or subtype of tumor, particularly in personalized medicine.

As stated in The BMJ 2009, tumor markers should not generally be used for the purpose of diagnosis of cancers, as opposed to monitoring purposes in certain cancers, or in certain cases, for screening purposes. The use of these tests without understanding their utility has resulted in inappropriate use of tumor marker blood tests, which has resulted in inappropriate over-investigation for cancers.

Techniques

Tumor markers can be determined in serum or rarely in urine or other body fluids, often by immunoassay, ⁣⁣ but other techniques such as enzyme activity determination are sometimes used. Microscopic visualization of tissue by immunohistochemistry does not give quantitative results and is not considered here.

For many assays, different assay techniques are available. For monitoring, it is important that the same assay is used, as the results from different assays are generally not comparable. For example, for AFP many different commercial assay kits, based on different technologies, are available and for thymidine kinase there are assays for either enzyme activity or amount of substance.

If repeated measurements of tumor marker are needed, some clinical testing laboratories provide a special reporting mechanism, a serial monitor that links test results and other data pertaining to the person being tested. This requires a unique identifier for the person. In the United States commonly a Social Security number & Civil Personal Record in Bahrain are used for this.

Interlaboratory proficiency testing for tumor marker tests, and for clinical tests more generally, is routine in Europe and an emerging field in the United States. New York state is prominent in advocating such research.

List of commonly used markers

Tumor marker	Associated tumor types
Alpha fetoprotein (AFP)	germ cell tumor, hepatocellular carcinoma
CA15-3	breast cancer
CA27.29	breast cancer
CA19-9	Mainly pancreatic cancer, but also colorectal cancer and other types of gastrointestinal cancer.
CA-125	Mainly ovarian cancer, but may also be elevated in for example endometrial cancer, fallopian tube cancer, lung cancer, breast cancer and gastrointestinal cancer. May also increase in endometriosis.
Calcitonin	medullary thyroid carcinoma
Calretinin	mesothelioma, sex cord-gonadal stromal tumor, adrenocortical carcinoma, synovial sarcoma
Carcinoembryonic antigen	gastrointestinal cancer, cervix cancer, lung cancer, ovarian cancer, breast cancer, urinary tract cancer
CD34	hemangiopericytoma/solitary fibrous tumor, pleomorphic lipoma, gastrointestinal stromal tumor, dermatofibrosarcoma protuberans
CD99MIC 2	Ewing sarcoma, primitive neuroectodermal tumor, hemangiopericytoma/solitary fibrous tumor, synovial sarcoma, lymphoma, leukemia, sex cord-gonadal stromal tumor
CD117	gastrointestinal stromal tumor, mastocytosis, seminoma
Chromogranin	neuroendocrine tumor
Chromosomes 3, 7, 17, and 9p21	bladder cancer
Cytokeratin (various types: TPA, TPS, Cyfra21-1)	Many types of carcinoma, some types of sarcoma
Desmin	smooth muscle sarcoma, skeletal muscle sarcoma, endometrial stromal sarcoma
Epithelial membrane antigen (EMA)	many types of carcinoma, meningioma, some types of sarcoma
Factor VIII, CD31 FL1	vascular sarcoma
Glial fibrillary acidic protein (GFAP)	glioma (astrocytoma, ependymoma)
Gross cystic disease fluid protein (GCDFP-15)	breast cancer, ovarian cancer, salivary gland cancer
hPG80	breast cancer, ovarian cancer, prostate cancer, kidney cancer, colorectal cancer, liver cancer
HMB-45	melanoma, PEComa (for example angiomyolipoma), clear cell carcinoma, adrenocortical carcinoma
Human chorionic gonadotropin (hCG)	gestational trophoblastic disease, germ cell tumor, choriocarcinoma
immunoglobulin	lymphoma, leukemia
inhibin	sex cord-gonadal stromal tumor, adrenocortical carcinoma, hemangioblastoma
keratin (various types)	carcinoma, some types of sarcoma
lymphocyte marker (various types)	lymphoma, leukemia
MART-1 (Melan-A)	melanoma, steroid-producing tumors (adrenocortical carcinoma, gonadal tumor)
Myo D1	rhabdomyosarcoma, small-blue-round-cell tumor
muscle-specific actin (MSA)	myosarcoma (leiomyosarcoma, rhabdomyosarcoma)
neurofilament	neuroendocrine tumor, small-cell carcinoma of the lung
neuron-specific enolase (NSE)	neuroendocrine tumor, small-cell carcinoma of the lung, breast cancer
placental alkaline phosphatase (PLAP)	seminoma, dysgerminoma, embryonal carcinoma
prostate-specific antigen (PSA)	prostate
PTPRC (CD45)	lymphoma, leukemia, histiocytic sarcoma
S100 protein	melanoma, sarcoma (neurosarcoma, lipoma, chondrosarcoma), astrocytoma, gastrointestinal stromal tumor, salivary gland cancer, some types of adenocarcinoma, histiocytic tumor (dendritic cell, macrophage)
smooth muscle actin (SMA)	gastrointestinal stromal tumor, leiomyosarcoma, PEComa
synaptophysin	neuroendocrine tumor
thymidine kinase	lymphoma, leukemia, lung cancer, prostate cancer
thyroglobulin (Tg)	post-operative marker of thyroid cancer (but not in medullary thyroid cancer)
thyroid transcription factor-1 (TTF-1)	all types of thyroid cancer, lung cancer
Tumor M2-PK	colorectal cancer, Breast cancer, renal cell carcinoma lung cancer, pancreatic cancer, esophageal cancer, stomach cancer,cervical cancer, ovarian cancer,
vimentin	sarcoma, renal cell carcinoma, endometrial cancer, lung carcinoma, lymphoma, leukemia, melanoma

Precision and accuracy

The required precision and accuracy for different analytes varies: some analytes give small or moderate changes in concentration or activity, thereby requiring high accuracy and precision to be useful, while others that show large differences between normal and pathological values may be useful even if the precision and accuracy are inferior. Therefore, the required precision and accuracy for a given assay may be different for different applications, such as in different diagnoses or for different uses. This also influences the useful working range for a given assay for different diagnosis or uses. Every laboratory should verify the precision and accuracy of the assays with the instruments and personnel used.

The high dose hook effect is an artifact of immunoassay kits, that causes the reported quantity to be incorrectly low when the quantity is high. An undetected hook effect may cause delayed recognition of a tumor. The hook effect can be detected by analyzing serial dilutions. The hook effect is absent if the reported quantities of tumor marker in a serial dilution are proportional to the dilution.

Multiple Tumor marker test

As with other diagnostic tests, tumor markers have a few test characteristics that influence their usability:

• Imperfect sensitivity, which would result in false negative tests, i.e. the test result is reassuring, but cancer is present or has recurred or progressed.
• Imperfect specificity, resulting in false positive tests, i.e. no cancer is present, but the test result indicates the opposite, resulting in needless further testing or anxiety.

As with other tests, predictive value (the chance that a positive or negative result represents the truth), depends strongly on the pre-test probability. The predictive value may be increased if two or more tests are carried out in parallel. The condition is that the tests have in themselves similar predictive values.

Test combinations that will give more exact results are for instance:

• Colorectal: M2-PK; if M2-PK is not available, can test CEA, CA 19–9, CA 125
• Breast: CEA, CA 15–3, Cyfra 21-1
• Ovary: CEA, CA 19–9, CA 125, AFP, BHCG
• Uterine: CEA, CA 19–9, CA 125, Cyfra 21–1, SCC
• Prostate: PSA, FPSA and ratio
• Testicle: AFP, BHCG
• Pancreas/Stomach: CEA, CA 19–9, CA 72-4
• Liver: CEA, AFP
• Oesophagus: CEA, Cyfra 21-1
• Thyroid: CEA, NSE
• Lung: CEA, CA 19–9, CA 125, NSE, Cyfra 21-1 (Sensitivity at 95 percent percentile for Cyfra 21-1 is 79 percent, while for SCC and CEA are 41 and 31 percent respectively)
• Bladder: CEA, Cyfra 21–1, TPA