Anion Gap

Serum anion gap, with optional albumin correction

Sodium (mmol/L)

Chloride (mmol/L)

Bicarbonate (mmol/L)

Albumin (g/dL) — optional, for correction

Enter sodium, chloride, and bicarbonate to calculate

Evidence

Original publication

Emmett M, Narins RG. Clinical use of the anion gap. Reviews the anion gap AG = Na⁺ − (Cl⁻ + HCO₃⁻), its normal range, and the differential for a high-gap versus normal-gap metabolic acidosis.

Medicine (Baltimore), 1977

Open source

Validation

Figge J, Jabor A, Kazda A, Fencl V. Anion gap and hypoalbuminemia. Each 1 g/dL fall in serum albumin lowers the measured anion gap by ~2.5 mmol/L, so the gap should be corrected upward in hypoalbuminaemic patients.

Critical Care Medicine, 1998

Open source

Last reviewed: 2026-09

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