Serum Anion Gap
Enter serum electrolytes (Na⁺, optional K⁺, Cl⁻, HCO₃⁻) and albumin to calculate the anion gap and assess metabolic acidosis.
Optional, improves accuracy
Corrects anion gap for hypoalbuminemia
Anion gap
16.0 mEq/L
Albumin-corrected gap
16.0 mEq/L
Mildly elevated anion gap
How to Use This Calculator
Obtain serum electrolytes
Use the latest metabolic panel. Include potassium for the full gap if available; otherwise the calculator assumes K⁺ 0.
Adjust for albumin
Hypoalbuminemia lowers the measured gap. The calculator corrects using +2.5 mEq/L per 1 g/dL albumin below 4.
Interpret with clinical context
Combine the anion gap with acid-base status, lactate, ketones, renal function, and clinical presentation to identify the cause.
Formula
Anion gap = Na⁺ + K⁺ − Cl⁻ − HCO₃⁻ (K⁺ optional)
Albumin-adjusted gap = AG + 2.5 × (4 − albumin)
Normal AG ≈ 12 ± 4 mEq/L (with potassium). Adjust reference ranges to local laboratory values.
Full Description
The serum anion gap represents unmeasured anions in plasma and is essential for diagnosing metabolic acidosis. Elevated gaps indicate accumulation of acids such as lactate, ketones, or toxins. Correcting for albumin prevents underestimation of the gap in hypoalbuminemia. Use the anion gap alongside delta-gap analysis, acid-base interpretation, and clinical context to narrow differential diagnoses.
Frequently Asked Questions
Should potassium always be included?
Many clinicians omit K⁺ because it minimally impacts the gap. Including it (if available) aligns with traditional definitions.
What are the causes of high anion gap acidosis?
Use mnemonics like GOLD MARK (Glycols, Oxoproline, L-lactate, D-lactate, Methanol, Aspirin, Renal failure, Ketoacidosis) to remember differentials.
How does hypoalbuminemia affect the gap?
Albumin is a major unmeasured anion. Low albumin lowers the gap; correction prevents falsely “normal” gaps in critically ill patients.
Can a normal gap exist with metabolic acidosis?
Yes, non-anion gap (hyperchloremic) acidosis occurs with diarrhoea, renal tubular acidosis, or saline infusion. Evaluate chloride and bicarbonate trends.