Anion Gap Calculator
Calculate serum anion gap and correct for albumin to evaluate metabolic acidosis
Clinical Interpretation
An elevated anion gap suggests accumulation of unmeasured organic acids (e.g. lactic acid, ketoacids). Correcting for albumin is essential in patients with hypoalbuminemia, as a drop in albumin by 1 g/dL lowers the normal anion gap by 2.5 mEq/L.
Mathematical Metric
Evidence & Lit
References: Emmett M, Narins RG. Clinical use of the anion gap. Medicine 1977.
Emmett & Narins, Medicine 1977 (PMID: 413723) →Frequently Asked Questions
What is the serum Anion Gap?
The serum anion gap is a calculated metric representing the difference between measured cations (sodium) and measured anions (chloride and bicarbonate). It helps identify the cause of metabolic acidosis.
What is a normal serum Anion Gap?
A normal anion gap is typically 8 to 12 mEq/L (without potassium). However, reference ranges vary slightly by laboratory and assay methods.
Why is it important to correct the Anion Gap for albumin?
Albumin is the major unmeasured anion in serum. For every 1 g/dL decrease in serum albumin below the normal value of 4.0 g/dL, the baseline anion gap decreases by approximately 2.5 mEq/L. Failing to correct for low albumin can mask an underlying high-gap acidosis.
What causes a high Anion Gap metabolic acidosis (HAGMA)?
HAGMA is caused by accumulation of unmeasured acid anions. Common etiologies can be recalled using the GOLD MARK mnemonic: Glycols, Oxoproline, L-lactate, D-lactate, Methanol, Aspirin (salicylates), Renal failure, and Ketoacidosis.