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Anion Gap
Anion gap calculation to differentiate metabolic acidosis — essential in ICU and emergency
Emergency
⚕️
Clinical reference only. Not a substitute for professional medical judgment. Verify all results against institutional protocols before clinical use.
Calculate
Anion gap must be interpreted alongside pH, lactate, clinical history and other electrolytes. Not a stand-alone diagnosis.
Formula
AG = Na⁺ − (Cl⁻ + HCO₃⁻) Albumin-corrected AG = AG + 2.5 × (4 − albumin[g/dL])
Na⁺Serum sodium (mEq/L)
Cl⁻Serum chloride (mEq/L)
HCO₃⁻Serum bicarbonate (mEq/L)
AlbuminSerum albumin (for correction) (g/dL)
When to Use
Metabolic acidosis workup, ICU electrolyte interpretation, toxicology screening, DKA/AKA management.
Clinical Pearls
- •Always correct AG for albumin — hypoalbuminaemia lowers the AG and can mask a true high-AG acidosis.
- •Delta-delta ratio: (AG − 12) / (24 − HCO₃) >2 suggests concurrent metabolic alkalosis.
- •Lactate is the most common cause of high-AG acidosis in critically ill patients.
- •DKA can present with near-normal glucose in patients who took insulin before presentation.
Original Publication
Emmett M (1977). Medicine.