Anion Gap Calculator

Calculate the anion gap and the albumin-corrected anion gap from sodium, chloride, bicarbonate and albumin. Educational tool only.

Sodium (Na⁺)

mmol/L

Chloride (Cl⁻)

mmol/L

Bicarbonate (HCO₃⁻)

mmol/L

AlbuminOptional. Used for the albumin-corrected gap.

g/L

Anion gap

14.0 mmol/L

Within the usual reference range of roughly 8–16 mmol/L

Albumin-corrected anion gap

14.0 mmol/L

Adjusted for an albumin of 40 g/L

A normal anion gap is roughly 8–16 mmol/L, though the exact range depends on the analyser and local reference intervals. A raised gap suggests extra unmeasured acid; a low gap can follow a low albumin, which is why the corrected figure is often more useful.

Frequently asked questions

What is a normal anion gap?

A normal anion gap is commonly quoted as about 8 to 16 mmol/L, though local laboratory reference ranges vary. Always compare against the range your lab reports.

What causes a raised anion gap?

A raised anion gap suggests an accumulation of unmeasured acids. Common causes are grouped under the mnemonic KULT or GOLD MARK, including ketones, lactate, urate, and toxins such as methanol or ethylene glycol.

Why correct the anion gap for albumin?

Albumin is a major negatively charged protein, so low albumin lowers the measured gap and can mask a real acidosis. The correction adds 2.5 mmol/L to the gap for every 10 g/L that albumin falls below 40 g/L.

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