Anion Gap Calculator (Metabolic Acidosis Workup)
Calculate serum anion gap and delta-delta ratio from electrolytes to help classify the type of metabolic acidosis.
Reviewed by Rahul Singh, Health & Wellness Specialist
Formula
AG = Na - (Cl + HCO3) | Corrected AG = AG + 2.5 × (4.0 - Albumin) | Delta Ratio = (Corrected AG - 12) / (24 - HCO3)
The anion gap measures unmeasured anions. Normal AG is 8-12 mEq/L. Corrected AG adjusts for hypoalbuminemia (2.5 mEq/L per 1 g/dL below 4.0). The delta-delta ratio identifies mixed acid-base disorders: <1 = concurrent NAGMA, 1-2 = pure HAGMA, >2 = concurrent metabolic alkalosis.
Worked Examples
Example 1: Elevated Anion Gap
Problem:Na 140, Cl 103, HCO3 24, Albumin 4.0 g/dL.
Solution:AG = 140 - (103 + 24) = 13\nCorrected AG = 13 + 2.5(4.0 - 4.0) = 13\nCorrected AG 13 > 12 mEq/L — Elevated (HAGMA)\nNormal range is 8-12 mEq/L
Result:AG 13, Corrected AG 13 — Elevated (HAGMA)
Example 2: DKA with HAGMA
Problem:Na 138, Cl 98, HCO3 10, Albumin 3.0 g/dL.
Solution:AG = 138 - (98 + 10) = 30\nCorrected AG = 30 + 2.5(4.0 - 3.0) = 32.5\nDelta ratio = (32.5 - 12)/(24 - 10) = 1.46\nPure HAGMA (ratio 1-2)
Result:AG 30, Corrected AG 32.5 — HAGMA, delta ratio 1.46 (pure HAGMA)
Frequently Asked Questions
What is the anion gap?
The anion gap is the difference between measured cations (sodium) and measured anions (chloride + bicarbonate) in the blood. It represents unmeasured anions such as albumin, phosphate, sulfate, and organic acids. The normal anion gap is approximately 8-12 mEq/L (when not corrected for albumin). An elevated anion gap indicates accumulation of unmeasured acids, as seen in conditions like DKA, lactic acidosis, and toxic ingestions.
What causes a high anion gap metabolic acidosis?
The mnemonic MUDPILES helps remember causes: Methanol, Uremia, Diabetic ketoacidosis (DKA), Propylene glycol, Isoniazid/Iron, Lactic acidosis (type A from tissue hypoperfusion, type B from medications or metabolic causes), Ethylene glycol, Salicylates. Other causes include starvation ketosis, alcoholic ketoacidosis, and toxic alcohol ingestions.
What is the anion gap and how is it calculated?
Anion gap = Sodium - (Chloride + Bicarbonate). Normal range is 8-12 mEq/L. An elevated anion gap indicates metabolic acidosis from conditions like diabetic ketoacidosis, lactic acidosis, renal failure, or toxic ingestions (MUDPILES mnemonic). A normal anion gap acidosis suggests GI or renal bicarbonate loss.
References
Reviewed by Rahul Singh, Health & Wellness Specialist · Editorial policy