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Anion Gap Calculator
Calculate anion gap from sodium, chloride, and bicarbonate with optional albumin correction and clinical interpretation.
Enter only if you want the albumin-corrected value (normal: 4.0 g/dL).
Reference Ranges
Low
Hypoalbuminemia, bromide, lithium
< 8 mEq/L
Normal
No evidence of AG acidosis
8 – 12 mEq/L
Mildly elevated
Consider clinical context
13 – 20 mEq/L
High
High-AG metabolic acidosis (MUDPILES)
> 20 mEq/L
Frequently Asked Questions
What is the anion gap?+
The anion gap (AG) is a calculated parameter from serum electrolytes: AG = Na⁺ − (Cl⁻ + HCO₃⁻). It helps narrow the cause of metabolic acidosis.
Why is albumin correction important?+
Albumin contributes to negative charge in serum. In hypoalbuminemia the AG is falsely low. The formula AG + 2.5 × (4.0 − albumin) corrects for this effect.
What are the most common causes of a high anion gap?+
MUDPILES: Methanol, Uremia, Diabetic Ketoacidosis (DKA), Propylene glycol, Iron/Isoniazid, Lactic acidosis, Ethylene glycol, Salicylates.
What causes a low anion gap?+
An AG < 8 mEq/L is most often caused by hypoalbuminemia, hyperchloremia, bromide intoxication, or lithium therapy. Measurement error is also possible.
Does this calculator replace medical diagnosis?+
No. The anion gap is a tool for clinical differential diagnosis and must always be interpreted in the context of history, symptoms, and other laboratory values.
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Background
Anion Gap Calculator — Understanding Metabolic Acidosis
8 min