Veterinary Hematology and Clinical Chemistry by unknow

Author:unknow
Language: eng
Format: epub
Publisher: Wiley
Published: 2012-06-26T04:00:00+00:00

Anion Gap

We measure several anions and cations in the blood, but there are many others that are not routinely measured. The predominant cations of ECF are sodium, potassium, calcium, and magnesium and the predominant anions are chloride, bicarbonate, plasma proteins, organic acid ions, phosphate, and sulfate. The number of unmeasured anions is greater than the number of unmeasured cations, and the difference between these is called the anion gap. The greatest change in the anion gap is when an elevation occurs due to an increase of organic acids in the circulation. The anion gap, therefore, is important in determination of the acid-base status of an animal (Chapter 25). The anion gap is essentially used to determine the cause of decreased blood bicarbonate concentrations (metabolic acidosis) or to detect metabolic acidosis during a mixed acid-base disorder in which bicarbonate may be normal or increased.

An indirect method is used to calculate the anion gap (Box 24.6). The calculation is based on the law of electroneutrality (The number of positive charges need to equal the number of negative charges in the body). The cations and anions that are considered “measured” are (a) sodium and potassium and (b) chloride and bicarbonate, respectively. The anion gap is the difference between these anions and cations as illustrated in Figure 24.5.

Box 24.6 Calculation of the Anion Gap.

Anion Gap Calculation

Given the law of electroneutrality (where UC is unmeasured cations and UA is unmeasured anions):

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