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Clinical — Acid-Base

Anion Gap Calculator

Enter sodium, chloride and bicarbonate to get the serum anion gap — with an optional albumin correction for a low albumin.

Filed by The Statistics Desk  |  Method: sodium minus (chloride + bicarbonate)
Anion gap
—
Sodium minus chloride and bicarbonate.
Acid-base readout
Albumin-corrected gap +2.5 per g/dL deficit—
Interpretation normal 8–12—
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How the Anion Gap Calculator Works

The serum anion gap estimates the difference between unmeasured anions and cations, calculated as sodium minus the sum of chloride and bicarbonate. A raised gap points toward a high anion gap metabolic acidosis — from lactate, ketones, kidney failure or certain toxins.

A low albumin lowers the measured gap, so when albumin is below normal the corrected gap adds about 2.5 for every 1 g/dL of albumin deficit. Enter albumin to apply this correction and avoid missing a true high-gap acidosis.

anion gap = sodium − (chloride + bicarbonate)

Frequently Asked Questions

What is a normal anion gap?

Roughly 8 to 12 mEq/L with most modern analyzers, though the normal range varies by lab. A raised gap suggests a high anion gap metabolic acidosis.

Should I correct for albumin?

Yes, when albumin is low. Each 1 g/dL drop in albumin lowers the measured gap by about 2.5, which can mask a true high-gap acidosis. Enter albumin to apply the correction.

Does this formula include potassium?

No, it uses the common formula: sodium minus chloride and bicarbonate. Some labs include potassium, which raises the normal range by about 4.

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