Why correct the anion gap for albumin?

Albumin is a negatively charged protein that contributes to the anion gap. In hypoalbuminemia, the measured anion gap is falsely low. For every 1 g/dL decrease in albumin below 4 g/dL, add 2.5 mEq/L to the anion gap.

Anion Gap Calculator

Q: What is the normal anion gap?

The normal anion gap is 8–12 mEq/L. Values above 12 mEq/L suggest a high anion gap metabolic acidosis. Values below 8 mEq/L may indicate hypoalbuminemia or other conditions.

Q: What causes a high anion gap?

Common causes of high anion gap metabolic acidosis include DKA (diabetic ketoacidosis), lactic acidosis, uremia, and toxic ingestions such as methanol, ethylene glycol, or salicylates — remembered by the MUDPILES mnemonic.

Calculate the anion gap and corrected anion gap using serum sodium, chloride, and bicarbonate. Includes albumin correction and clinical interpretation based on the normal range of 8–12 mEq/L.

Anion Gap Calculator

Sodium — Na⁺ (mEq/L)

Chloride — Cl⁻ (mEq/L)

Bicarbonate — HCO₃⁻ (mEq/L)

Albumin (g/dL) — optional, for correction

What Is the Anion Gap?

The anion gap (AG) is a calculated value used in medicine to assess acid-base disorders, particularly metabolic acidosis. It represents the difference between measured cations (positively charged ions) and measured anions (negatively charged ions) in serum. The unmeasured anions include albumin, phosphate, sulfate, and organic acids.

Anion Gap Formula

AG = Na⁺ − (Cl⁻ + HCO₃⁻) Normal Range: 8–12 mEq/L Corrected AG (for albumin): AG_corrected = AG + 2.5 × (4.0 − measured albumin in g/dL)

Interpretation Guide

Anion Gap	Interpretation
< 8 mEq/L	Low AG — possible hypoalbuminemia, hypermagnesemia, or lab error
8–12 mEq/L	Normal — no high anion gap acidosis
13–19 mEq/L	Mildly elevated — borderline, clinical correlation needed
≥ 20 mEq/L	High AG metabolic acidosis (MUDPILES: Methanol, Uremia, DKA, Propylene glycol, Isoniazid, Lactic acidosis, Ethylene glycol, Salicylates)

Clinical Importance

The anion gap is a critical tool in diagnosing metabolic acidosis. A high anion gap indicates that organic acids or other unmeasured anions are accumulating in the blood. The corrected anion gap is especially important in patients with hypoalbuminemia, as low albumin can mask a true high anion gap acidosis.

Disclaimer: This calculator is for educational and reference purposes only. Clinical decisions should always be made by qualified healthcare professionals using the full clinical picture.

Frequently Asked Questions

What is the normal anion gap?+

The normal anion gap is 8–12 mEq/L. Some labs report a slightly different reference range (6–14 mEq/L) depending on the assay used. Values consistently above 12 mEq/L warrant further investigation.

What causes a high anion gap acidosis?+

The MUDPILES mnemonic covers the main causes: Methanol, Uremia, DKA (diabetic ketoacidosis), Propylene glycol, Isoniazid/Iron, Lactic acidosis, Ethylene glycol, and Salicylates. Lactic acidosis and DKA are the most common causes.

When should I correct the anion gap for albumin?+

Albumin correction is important in critically ill patients, malnourished patients, and those with liver disease — all groups prone to hypoalbuminemia. A normal albumin is 4.0 g/dL. For each 1 g/dL decrease, add 2.5 mEq/L to the measured AG.

Anion Gap Calculator

What Is the Anion Gap?

Anion Gap Formula

Interpretation Guide

Clinical Importance

Frequently Asked Questions

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