The serum anion gap is the difference between the concentrations of the major cation, sodium and the major anions(Cl + HCO3). An electrolyte abnormality is often the first laboratory sign of an acid-base disorder. The anion gap measurement is likely to be most useful in emergency department in cases with ketoacidosis, lactic acidosis or renal failure.
- Normal Values:
mmol/L (Only values < 2 and > 17 mmol/L are likely to be clinically significant).
Acidosis can occur even when the anion gap is normal, as in the following cases:
- gastrointestinal HCO3 loss; diarrhoea, fistulas etc.
- increased Chloride; uterosigmoidostomy etc.
- renal tubular acidosis
- drugs, eg acetozolamide
- administration of ammonium chloride
- Increased anion gap could indicate:
- renal failure:
- increase in phosphate, sulphate
- diabetic ketoacidosis,starvation ketoacidosis
- lactic acidosis
- methanol - formic acid metabolite
- ethylene glycol - oxalic/glycolic acids
- aspirin - salicylic acid
In practice, an increased anion gap is usually due to an accumulation of unmeasured anions.
- Decreased anion gap could indicate:
- marked increase in the cations.
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