Anion gap is calculated as the difference between the sum of cations and anions found in plasma and serum. This calculated sum is representative of the unmeasured ions in the plasma or serum. This article on how to calculate anion gap will help you in calculating anion gap using simple formulae. There are also online calculators for calculating anion gap.
- The commonly measured cations while calculating the anion gap include sodium, calcium, magnesium and potassium. While the commonly measured anions included in this calculation are bicarbonate, chlorine and phosphate.
- Certain unmeasured cations and anions such as naturally occurring serum proteins and sulphates are also used in the calculation of anion gap.
There are two methods of calculating the anion gap viz. with potassium and without potassium.
- Calculating anion gap with potassium
While calculating anion gap with potassium, we subtract the serum concentrations of chloride and bicarbonate from the sodium and potassium. Here, chloride and bicarbonate are anions and sodium and potassium are cations.
Therefore anion gap in this case is given by:
Anion gap = ([Na+] + [K+]) − ([Cl−] + [HCO3−])
- Calculating anion gap without potassium
Concentration of potassium in the serum is very low which is negligible. Hence, during the calculation of anion gap the concentration of potassium is frequently ignored. Even if we eliminate the potassium concentration from the formulae there is a little effect on the calculation.
Anion gap in this case is given by the formula:
Anion gap = ([Na+]) − ([Cl−] + [HCO3−])
Where,
- Na+ = sodium
- K+ = Potassium
- Cl- = Chlorine
- HCO3 - = Bicarbonate
- The unit for measuring the anion gap is milliequivalents/liter (mEq/L) or millimoles/liter (mmol/L).
- If the anion gap is positive, then the person is considered to be healthy. An anion gap of 8 to 12 mEq/L in case of adults is considered to be normal.
- Calculation of anion gap helps in diagnosis of a large number of diseases; it helps in differential diagnosis of the disease.
- This anion gap varies according to the concentration of the components of the serum; mostly changes in unmeasured ions affect the value of anion gap.
- The value of anion gap may be considered as high if it is above 12 mEq/L and a high anion gap indicates acidosis. There is a decrease in the bicarbonate concentrations and this is replaced by the unmeasured anions increasing the anion gap.
- If the value of anion gap is below 8 mEq/L then it is considered as low anion gap. This happens mainly because of the decreased level of albumin from the serum. Albumin is a negatively charged protein and its loss results in retention of chloride and bicarbonate in the body, thus decreasing the anion gap.
- There are online calculators also available on the internet which can calculate your anion gap. You need to measure the concentration of anion and cations in the serum and put them in the text boxes provided in proper units, click a button and you will get your anion gap calculated.
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