Anion Gap

Anion gap calculation is a useful aid that may assist in the differential diagnosis of metabolic acidosis. The anion gap is the difference in the concentrations between the major plasma major cations (sodium, potassium) and the two major anions (chloride, bicarbonate). Sodium and potassium make up ~90% of the plasma anions; the remainder is mainly calcium, magnesium and some proteins (gamma globulins). Chloride and bicarbonate comprise around 80% of the plasma anions; the remainder include negatively charged proteins (mostly albumin), lactate and urate.The anion gap is calculated in the laboratory using the following equation. All measurements are in mmol/L:Anion gap= [sodium] + [potassium] – [chloride] – [bicarbonate]