Anion gap calculator
Serum anion gap with the albumin correction, which is omitted more often than not.
Optional. Supply it to see the corrected gap.
Less common. Raises the gap by roughly the potassium value.
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This is a reference implementation of a published formula, provided for use by qualified healthcare professionals. It does not diagnose, does not account for the individual circumstances of any patient, and is not a recommendation for treatment. Confirm every result against your own institutional guidance before acting on it. Clinical judgement always takes precedence over a calculator.
About this calculation
The anion gap is the difference between measured cations and measured anions, used to classify a metabolic acidosis. Albumin is itself an unmeasured anion, so in a hypoalbuminaemic patient the uncorrected gap can look normal while a raised-gap acidosis is present.
Formula
Anion gap = Na⁺ − (Cl⁻ + HCO₃⁻). Corrected = AG + 2.5 × (4.0 − albumin g/dL)
- Source
- Figge J et al., Journal of Laboratory and Clinical Medicine — albumin correction (1998)
- Methodology version
- 1.0.0
- Last reviewed
- 2026-10-28
What this does not account for
- Reference ranges for the anion gap vary between laboratories and with the analyser used. Use your own laboratory’s range.
- Including potassium raises the gap by roughly its serum value; the two conventions are not comparable, so be consistent.
- A normal corrected gap does not exclude a mixed disorder. A delta ratio may be needed alongside it.