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Calculates the albumin-corrected anion gap. In hypoalbuminemia, the measured anion gap is falsely low, potentially masking a high anion gap metabolic acidosis. This correction adjusts for the albumin contribution.
Corrected AG = (Na − (Cl + HCO₃)) + 2.5 × (4 − Albumin)
8–12 mmol/L
Interpret results together with the patient's clinical presentation.
Specialty
Internal MedicineCategory
Internal MedicineDifficulty
Basic
Estimated Time
30 seconds
Version
1.0
Last Updated
2026-08-06
Formula
Keywords
Normal Range
8–12 mmol/L
| Classification | Range |
|---|---|
Low corrected anion gap | <7.1 |
Normal corrected anion gap | 8–12 |
High corrected anion gap | ≥13 |
Markedly elevated corrected anion gap | ≥20 |
Adjusts the serum anion gap for hypoalbuminemia to unmask a hidden high anion gap metabolic acidosis (HAGMA) that a low albumin would otherwise conceal.
A corrected anion gap of 8–12 mmol/L is normal. ≥13 mmol/L indicates a high corrected anion gap, and ≥20 mmol/L is markedly elevated. Each 1 g/dL drop in albumin below 4.0 g/dL lowers the measured anion gap by roughly 2.5 mmol/L.
Albumin normally contributes roughly 75% of the anion gap. In hypoalbuminemia the measured gap is falsely low, so correction is essential in critically ill patients where a HAGMA could otherwise be missed.
A 62-year-old ICU patient has sodium 140 mmol/L, chloride 105 mmol/L, bicarbonate 12 mmol/L, and albumin 3.0 g/dL.
Inputs:
Corrected AG = (140 − (105 + 12)) + 2.5 × (4 − 3) = 23 + 2.5 = 25.5 mmol/L — markedly elevated, consistent with a high anion gap metabolic acidosis.
Albumin is a negatively charged protein that contributes significantly to the normal anion gap. When albumin is low, there are fewer unmeasured negative charges, so the calculated gap falls even when an acidosis is present.
The most common correction adds 2.5 mmol/L to the measured anion gap for every 1 g/dL that albumin falls below 4.0 g/dL. Some sources use 2.4 or 2.8 mmol/L per g/dL depending on the population.
Disclaimer: This calculator is intended for educational and clinical decision support purposes only. Interpret the corrected anion gap together with arterial blood gas and the clinical context.