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Anion gap calculator

Calculate the serum anion gap with or without potassium, adjust for albumin, or solve for a missing electrolyte concentration.

Enter the numeric value in the selected unit. This selector changes how the value is interpreted.

Unadjusted anion gap (mmol/L)
12.00
Albumin-adjusted gap (mmol/L)
12.00
Sodium (mmol/L)
140.00
Chloride (mmol/L)
104.00
Bicarbonate (mmol/L)
24.00
Albumin (g/L)
40.00

Estimates for information only. Not financial, medical, legal or engineering advice. See the Terms.

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How this calculator works

Choose one missing quantity and use a consistent set of laboratory samples. Including potassium changes the gap and its reference interval. Albumin is converted to g/L before adjustment. A negative calculated gap is retained because analytical artefacts and uncommon clinical situations can produce it. The result is an estimate for information only and is not medical advice.

Formula

AG = Na + K - Cl - HCO3 when potassium is included; otherwise omit K. Adjusted AG = AG + 0.25(40 - albumin in g/L). Rearrange the same equation for the selected unknown.

Worked example

140 - 104 - 24 = 12 mmol/L. Albumin 30 g/L adds 2.5, giving 14.5. Including potassium 4 mmol/L gives an unadjusted gap of 16.

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Frequently asked questions

Is potassium normally included?

Many laboratories omit it. Match the equation and reference interval used by the reporting laboratory.

Can I compare mmol/L with mEq/L?

For these monovalent ions, the numerical values are equal. Albumin uses a mass concentration instead.

Is an elevated gap a diagnosis?

No. Laboratory methods, albumin and the clinical context affect interpretation. This page does not apply a universal high-gap threshold.

Sources

Written byAmira MansourCalculator writer. Builds and tests Mathulate calculators against published sources.
Reviewed byPriya Natarajan, RDRegistered dietitian. Checks health calculators against public health guidance.

Last updated .

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