What is the anion gap?

The anion gap represents unmeasured anions in blood. It's calculated as Na⁺ - (Cl⁻ + HCO₃⁻). Normal range is 8-12 mEq/L. A high anion gap indicates presence of unmeasured anions like lactate, ketones, or toxins.

Why do we correct for albumin?

Albumin is the major unmeasured anion contributing to the normal anion gap. For every 1 g/dL decrease in albumin below 4 g/dL, the anion gap decreases by ~2.5 mEq/L. Without correction, a high AG acidosis could be missed in hypoalbuminemic patients.

MUDPILES is a mnemonic for causes of high anion gap metabolic acidosis: Methanol, Uremia, DKA (diabetic ketoacidosis), Propylene glycol, Isoniazid/Iron, Lactic acidosis, Ethylene glycol, Salicylates. Also remember KULT: Ketoacidosis, Uremia, Lactic acidosis, Toxins.

What causes a low anion gap?

Low AG (<3-4) can be caused by: hypoalbuminemia (most common), multiple myeloma (cationic paraproteins), lithium toxicity (increases unmeasured cations), or laboratory error. A very low anion gap should prompt investigation.

What is the delta-delta or delta ratio?

Delta ratio = Δ Anion Gap / Δ Bicarbonate = (AG - 12) / (24 - HCO₃). It helps identify mixed acid-base disorders. 2: HAGMA + metabolic alkalosis. Only use in confirmed HAGMA.

What is a non-anion gap metabolic acidosis (NAGMA)?

NAGMA occurs when bicarbonate is lost and replaced by chloride, keeping AG normal. Causes (HARDUPS): Hyperalimentation, Acetazolamide, RTA, Diarrhea, Ureteral diversions, Pancreatic fistula, Saline administration.

Anion Gap Calculator

Q: What causes a low anion gap?

Low AG (<3-4) can be caused by: hypoalbuminemia (most common), multiple myeloma (cationic paraproteins), lithium toxicity (increases unmeasured cations), or laboratory error. A very low anion gap should prompt investigation.

Q: What is the delta-delta or delta ratio?

Delta ratio = Δ Anion Gap / Δ Bicarbonate = (AG - 12) / (24 - HCO₃). It helps identify mixed acid-base disorders. 2: HAGMA + metabolic alkalosis. Only use in confirmed HAGMA.

Q: What is a non-anion gap metabolic acidosis (NAGMA)?

NAGMA occurs when bicarbonate is lost and replaced by chloride, keeping AG normal. Causes (HARDUPS): Hyperalimentation, Acetazolamide, RTA, Diarrhea, Ureteral diversions, Pancreatic fistula, Saline administration.

Calculate anion gap and corrected anion gap for metabolic acidosis workup. Includes delta ratio interpretation.

Electrolytes

Sodium (Na⁺)

mEq/L

Serum sodium. Normal: 135-145 mEq/L. The main measured cation in the anion gap calculation. Also check for pseudohyponatremia in hyperlipidemia/hyperproteinemia.

Chloride (Cl⁻)

mEq/L

Serum chloride. Normal: 98-106 mEq/L. One of the measured anions. Elevated in non-anion gap metabolic acidosis (NAGMA). Decreased in metabolic alkalosis from vomiting.

Bicarbonate (HCO₃⁻)

mEq/L

Serum bicarbonate (can use CO₂ from BMP). Normal: 22-28 mEq/L. Decreased in metabolic acidosis; increased in metabolic alkalosis or respiratory compensation.

Albumin

g/dL

Serum albumin. Normal: 3.5-5.0 g/dL. Essential for correcting anion gap. Low albumin will lower the anion gap, potentially masking a HAGMA.

Anion Gap

— mEq/L

Enter electrolyte values

Corrected AG

—

Adjusted for albumin

Delta Gap

—

Excess above 12

Status

Low

The Formulas

Anion Gap

AG = Na⁺ - (Cl⁻ + HCO₃⁻)

= 140 - (104 + 24) = mEq/L

Corrected AG (for albumin)

Corrected AG = AG + 2.5 × (4 - Albumin)

= + 2.5 × (4 - 4) = mEq/L

Frequently Asked Questions

How to Use

About the Anion Gap Calculator

What it calculates

This anion gap calculator applies a validated clinical scoring method used in healthcare settings. Metabolic acidosis workup.

When to use it

Use as a clinical decision support aid alongside professional judgment — not as a standalone diagnosis.

Example

Adjust the inputs above to model your specific scenario with the Anion Gap Calculator.

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Anion Gap Calculator

Electrolytes

— mEq/L

The Formulas

About the Anion Gap Calculator

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