Why does albumin affect the anion gap?

Albumin carries a net negative charge at physiologic pH and is the main unmeasured anion in serum. A normal albumin of 4 g/dL contributes roughly 10–12 mEq/L to the anion gap. When albumin is low, the measured AG falls proportionally, potentially hiding a true acid accumulation. Correcting for albumin restores the clinical accuracy of the AG.

What is the albumin correction formula?

Corrected AG = Measured AG + 2.5 × (4.0 − serum albumin in g/dL). If albumin is 2 g/dL, the correction adds 2.5 × 2 = 5 mEq/L to the measured AG. A corrected AG ≥ 12 mEq/L is considered elevated.

What is the normal corrected anion gap?

A corrected AG below 12 mEq/L is generally considered normal. Values at or above 12 mEq/L indicate a high-AG metabolic acidosis. Some references use 12 ± 2 as the boundary; clinical context and arterial blood gas are required for full interpretation.

What causes a high corrected anion gap?

A corrected AG ≥ 12 mEq/L suggests acid accumulation from causes recalled by the MUDPILES mnemonic: Methanol, Uremia, Diabetic ketoacidosis, Propylene glycol/Paracetamol, Isoniazid/Iron, Lactic acidosis, Ethylene glycol, Salicylates. The GOLDMARK mnemonic (Glycols, Oxoproline, L-lactate, D-lactate, Methanol, Aspirin, Renal failure, Ketoacidosis) is a newer alternative.

Is this tool a substitute for clinical judgment?

No. This calculator is for educational and reference use only. All clinical decisions — including diagnosis and treatment — require correlation with arterial blood gas results, full clinical history, and evaluation by a qualified healthcare professional.

Corrected Anion Gap Calculator

Enter Na, Cl, HCO3, and serum albumin to calculate the albumin-corrected anion gap and detect high-AG metabolic acidosis masked by low albumin.

Serum Values

All values in mEq/L except albumin (g/dL)

Sodium (Na⁺) normal 135–145 mEq/L

Chloride (Cl⁻) normal 95–105 mEq/L

Bicarbonate (HCO₃⁻) normal 22–29 mEq/L

Serum Albumin g/dL — normal 4.0

Results

Enter values and click Calculate

Quick Reference

Corrected AG Interpretation

Corrected AG	Meaning
< 12 mEq/L	Normal — no high-AG acidosis
12–20 mEq/L	Mildly elevated — consider early HAGMA
> 20 mEq/L	High — significant HAGMA (MUDPILES)

Sample Calculation

Step	Value
Na=140, Cl=105, HCO3=20	AG = 15
Albumin = 2.0 g/dL	+2.5×(4−2) = +5
Corrected AG	15 + 5 = 20 (elevated)

For educational and reference use only. All clinical decisions require evaluation by a qualified healthcare professional.

Summary

In hypoalbuminemic patients, the standard anion gap underestimates the true acid burden because albumin itself is an unmeasured anion. The albumin-corrected anion gap adds 2.5 mEq/L for each 1 g/dL drop in albumin below 4 g/dL, revealing high-AG metabolic acidosis that would otherwise be missed. This is especially important in critically ill, cirrhotic, or malnourished patients whose albumin is chronically low.

How it works

Enter serum sodium (Na+), chloride (Cl−), and bicarbonate (HCO3−) in mEq/L.
Enter serum albumin in g/dL (normal is 4.0 g/dL).
The measured anion gap is calculated: AG = Na − (Cl + HCO3).
The albumin correction is applied: Corrected AG = AG + 2.5 × (4.0 − albumin).
Results are interpreted against the normal threshold of 12 mEq/L.
A medical disclaimer reminds you this tool is for reference only.

Use cases

Detecting high-AG metabolic acidosis in ICU patients with low albumin.
Acid-base workup in cirrhotic or liver-failure patients.
Evaluating metabolic acidosis in malnourished or cancer patients.
Medical education on albumin correction and anion gap physiology.
Confirming whether an apparently normal AG is truly normal in hypoalbuminemia.
Rapid bedside calculation when labs return in the emergency department.
Nephrology and critical care clinical decision support.
USMLE and board exam practice on acid-base disorders.

Frequently Asked Questions

Last updated: 2026-06-11 · Reviewed by Nham Vu