Anion Gap
A calculated value that helps detect unmeasured acids in the blood.
| Typical reference range | 3–14 mmol/L |
Ranges vary by laboratory, method, age and sex: always use the range printed on your own report. Why labs differ.
What it measures
The anion gap is sodium minus the sum of chloride and bicarbonate (some labs also add potassium). It estimates negatively charged substances not routinely measured, mostly albumin.
Why it matters
A raised anion gap signals accumulation of acids such as ketones, lactate or toxins, helping classify metabolic acidosis.
What a high result can mean
High values occur with ketoacidosis (diabetic, alcoholic or starvation), lactic acidosis, kidney failure and certain toxins (methanol, ethylene glycol, high-dose aspirin).
What a low result can mean
Low values are most often due to low albumin, and less commonly to high levels of certain antibodies (multiple myeloma) or lab error.
What affects the result
Reference ranges vary considerably by analyzer and whether potassium is included. Albumin should be considered when interpreting it.
Units and conversion
Usually reported in mmol/L.
- From mEq/L: multiply by 1 to get mmol/L
Also called on lab reports
Anion Gap (Calc), Anion Gap, Serum, AGAP
Related tests: Electrolytes & Minerals
This page is educational and does not replace advice from a healthcare professional.