Laboratory

Anion Gap

Calculates the serum anion gap to evaluate metabolic acidosis.

Parameters

mEq/L
mEq/L
mEq/L

Anion Gap Result

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FormulaAnion Gap = Na⁺ - (Cl⁻ + HCO₃⁻)

Clinical Pearls

A high anion gap indicates the presence of unmeasured anions (e.g., ketones, lactate, exogenous toxins). Common causes of High Anion Gap Metabolic Acidosis are remembered by the mnemonic MUDPILES (Methanol, Uremia, DKA, Paraldehyde, Iron/Isoniazid, Lactic acidosis, Ethylene glycol, Salicylates).

Normal Values / Reference

Normal anion gap is typically between 8 and 12 mEq/L (without potassium).

Limitations

The calculation depends on normal albumin levels. For every 1 g/dL decrease in albumin below 4.0 g/dL, the normal anion gap decreases by 2.5 mEq/L.