How do you calculate the albumin-corrected anion gap?

The corrected anion gap = Calculated anion gap + 2.5 × (4.0 − measured albumin in g/dL). For each 1 g/dL decrease in albumin below 4.0, the anion gap is increased by 2.5 mEq/L. This correction unmasks true anion gap elevations in hypoalbuminemic patients.

What is a normal albumin-corrected anion gap?

A normal albumin-corrected anion gap is 12 ± 4 mEq/L, similar to the normal uncorrected anion gap. Values above 16 mEq/L suggest an anion gap metabolic acidosis. The correction is most important in ICU patients where hypoalbuminemia is prevalent.

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Albumin-Corrected Anion Gap

Correct the anion gap for hypoalbuminemia. Albumin is an unmeasured anion — low levels can mask a true anion gap metabolic acidosis.

Inputs

Sodium (mEq/L)

Chloride (mEq/L)

Bicarbonate (mEq/L)

Serum Albumin (g/dL)

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Enter values to calculate.

Disclaimer: For educational purposes only. Not a substitute for clinical judgment.

When to use

Use whenever calculating the anion gap in a patient with hypoalbuminemia (common in hospitalized, critically ill, cirrhotic, or nephrotic patients). Low albumin lowers the anion gap by ~2.5 mEq/L for every 1 g/dL below 4.0.

Clinical pearls

Formula: Corrected AG = Calculated AG + 2.5 × (4.0 − measured albumin)
A patient with albumin 2.0 and AG of 12 has a corrected AG of 17 — an occult AGMA.
Always correct the AG for albumin in ICU patients where albumin is frequently low.
Proceed to delta-delta (Δ/Δ) ratio if corrected AG is elevated to identify mixed disorders.

References

Figge J, Jabor A, Kazda A, Fencl V. Anion gap and hypoalbuminemia. Crit Care Med. 1998;26(11):1807-1810.
Feldman M, et al. Influence of hypoalbuminemia or hyperalbuminemia on the serum anion gap. J Lab Clin Med. 2005;146(6):317-320.

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About This Tool

Why Correct the Anion Gap for Albumin?

Albumin is the major unmeasured anion in serum. The traditional anion gap formula (Na − Cl − HCO₃) has a normal range of ~12 mEq/L, which assumes a normal albumin of ~4.0 g/dL. Each 1 g/dL decrease in albumin reduces the anion gap by approximately 2.5 mEq/L. In critically ill patients where hypoalbuminemia is common, this can mask a significant anion gap metabolic acidosis.

The Formula

Corrected AG = (Na − Cl − HCO₃) + 2.5 × (4.0 − Albumin)

This correction was validated by Figge et al. in 1998 and is now standard practice in acid-base analysis, particularly in the ICU setting.

🔑 Clinical Pearls

In ICU patients, always correct the AG for albumin — up to 50% of AGMA cases can be missed without correction.
Example: Na 140, Cl 108, HCO₃ 22, Albumin 2.0 → AG = 10 (looks normal) → Corrected AG = 15 (elevated!).
After finding an elevated corrected AG, calculate the delta-delta ratio to identify mixed disorders.
The Stewart (physicochemical) approach to acid-base inherently accounts for albumin as a weak acid.

Key References

Figge J, Jabor A, Kazda A, Fencl V. Anion gap and hypoalbuminemia. Crit Care Med. 1998;26(11):1807-1810.
Kraut JA, Madias NE. Serum anion gap: its uses and limitations in clinical medicine. Clin J Am Soc Nephrol. 2007;2(1):162-174.

Formula last verified: February 2026