What is the normal anion gap?

The traditional normal range is 8–12 mEq/L with modern analyzers. Older references cite 12 ± 4 mEq/L. Values above 12 are generally considered elevated and warrant further workup.

What causes a high anion gap?

Common causes are recalled with MUDPILES: Methanol, Uremia, Diabetic ketoacidosis, Propylene glycol, Isoniazid/Iron, Lactic acidosis, Ethylene glycol, Salicylates. The newer GOLDMARK mnemonic adds Glycols, Oxoproline, L-lactate, D-lactate, Methanol, Aspirin, Renal failure, Ketoacidosis.

Why correct for albumin?

Albumin is a major unmeasured anion. Each 1 g/dL fall below 4 g/dL lowers the measured AG by roughly 2.5 mEq/L. Hypoalbuminemia can mask a true high-AG acidosis, so the corrected AG is more reliable in patients with liver disease, malnutrition, or critical illness.

How do I interpret the delta gap?

Delta gap = (AG − 12) / (24 − HCO3). A ratio 2 suggests a superimposed metabolic alkalosis.

Is this tool a substitute for clinical judgment?

No. This calculator is for educational and reference use only. Acid-base interpretation requires correlation with arterial blood gas, clinical history, and physical examination by a qualified clinician.

Should potassium be included in the anion gap?

Some labs use Na + K − (Cl + HCO3). Adding potassium raises the result by about 4 mEq/L, so that version has a higher normal range. This calculator leaves potassium out; compare your result with the range your lab reports.

What causes a low anion gap?

Low albumin is the most common cause. Others include IgG multiple myeloma, lithium or bromide exposure, and lab error. A gap below 8 mEq/L that is not explained by albumin is worth repeating.

Anion Gap Calculator

Enter Na, Cl, HCO3 (and optionally albumin) to get the anion gap, albumin-corrected AG, and delta gap for mixed acid-base disorder detection.

Anion gap = Na − (Cl + HCO3).

Serum Values

Required values in mEq/L (mmol/L)

Sodium (Na⁺) normal 135–145

Chloride (Cl⁻) normal 95–105

Bicarbonate (HCO₃⁻) normal 22–29

Albumin optional, g/dL — enables corrected AG

Results

Enter values and click Calculate

Quick Reference

Anion Gap Ranges

AG (mEq/L)	Classification
< 8	Low — hypoalbuminemia, hypermagnesemia
8 – 12	Normal
12 – 20	Mildly elevated — early DKA, lactic acidosis
> 20	High — severe HAGMA (DKA, toxic ingestion)

Delta Gap Ratio

Ratio	Interpretation
< 0.4	Pure normal-AG acidosis
0.4 – 1.0	Mixed high-AG + normal-AG acidosis
1.0 – 2.0	Pure high-AG metabolic acidosis
> 2.0	High-AG acidosis + metabolic alkalosis

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

Quick answer

Anion gap = Na − (Cl + HCO3). With current analyzers the normal range is about 8–12 mEq/L; above 12 points to a high-anion-gap metabolic acidosis. Low albumin hides a high gap, so add 2.5 for each 1 g/dL of albumin below 4.

Examples

Na	Cl	HCO3	Albumin	Anion gap
140	104	24	4.0	12 (normal)
135	98	10	4.0	27 (high), delta ratio 1.07
138	106	22	2.0	10, corrected 15 (high)

Enter Na, Cl and HCO3.

Summary

The anion gap (AG = Na − Cl − HCO3) quantifies unmeasured serum anions and is the first step in metabolic acidosis workup. Normal AG is 8–12 mEq/L; values above 12 suggest acid accumulation (DKA, lactic acidosis, uremia, toxic ingestion). When albumin is low, the corrected AG adjusts for hypoalbuminemia. The delta gap (delta AG / delta HCO3) detects a superimposed metabolic alkalosis or normal-AG acidosis hiding behind a high-AG picture.

How it works

Enter serum sodium (Na+), chloride (Cl−), and bicarbonate (HCO3−) in mEq/L.
Optionally enter serum albumin (g/dL) to get the albumin-corrected anion gap.
The calculator applies AG = Na − (Cl + HCO3) and classifies the result.
If albumin is provided, corrected AG = AG + 2.5 × (4 − albumin).
Delta gap = (AG − 12) / (24 − HCO3) detects mixed acid-base disorders.
Interpretation panels explain the clinical meaning of each result.

Use cases

Emergency workup of a patient with metabolic acidosis.
Distinguishing high-AG from normal-AG (hyperchloremic) metabolic acidosis.
Unmasking a coexisting metabolic alkalosis or normal-AG acidosis with the delta gap.
Adjusting for hypoalbuminemia in critically ill or cirrhotic patients.
Medical education and acid-base physiology study.
Serial monitoring of electrolyte trends in the ICU.

Frequently Asked Questions

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