Enter your patient's Sodium (Na⁺), Chloride (Cl⁻), Bicarbonate (HCO₃⁻), and optionally Potassium (K⁺) levels, choose your preferred formula type, and the Anion Gap Calculator will compute the anion gap value along with a clinical interpretation and the expected reference range.
Anion Gap
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Interpretation
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Reference Range
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Anion gap is the difference between measured cations and anions in serum. It helps diagnose metabolic acidosis and identify unmeasured anions like lactate, ketoacids, or toxic substances.
The normal anion gap range is typically 8-12 mEq/L for the standard formula (Na⁺ - Cl⁻ - HCO₃⁻) and 10-14 mEq/L when including potassium.
A high anion gap (>12 mEq/L) suggests metabolic acidosis with unmeasured anions present, such as in diabetic ketoacidosis, lactic acidosis, or poisoning with methanol or ethylene glycol.
Low anion gap (<8 mEq/L) can result from hypoalbuminemia, multiple myeloma with cationic proteins, lithium toxicity, or laboratory errors. It's less common but clinically significant.
Both formulas are valid. The standard formula excludes potassium as its concentration is relatively low and stable. Including potassium gives slightly higher values but both are diagnostically useful.
Anion gap should be calculated when evaluating acid-base disorders, unexplained metabolic acidosis, suspected poisoning, or monitoring patients with diabetes or kidney disease.