Anion Gap optimal range and reference range
Compiled by Alina Radu, founder of Sera, from the published sources below · Last reviewed November 9, 2026
Sera's bands for Anion Gap:
- Optimal 8 – 12 mmol/L; sufficient 6 – 14 mmol/L; out of range below 6 or above 14 mmol/L.
Evidence grade: Exploratory index. A calculated or emerging measure that can be useful for reviewing a pattern but has no universally accepted clinical threshold.
Read it as exploratory rather than diagnostic: there is no universally accepted cut-off, so these are Sera's current working bands.
All units
| Unit | Optimal | Sufficient | Out of range |
|---|---|---|---|
| mmol/L | 8 – 12 | 6 – 14 | below 6 or above 14 |
What the evidence says
The first branch point in an acid–base problem: a metabolic acidosis with a raised gap points at lactate, ketones, kidney failure or a toxin, while a normal gap points at bicarbonate loss from gut or kidney. It falls with low albumin, itself an unmeasured anion, so correct for albumin before calling a gap normal in an unwell client. Sera computes it without the potassium term, which is the more common of the two conventions. Read it as an exploratory index rather than a diagnostic test: published laboratory ranges for this formula run from 2 to 13 mmol/L to 7 to 15, depending on the analyser, and Sera's bands match none of them exactly.
Sources
- ELPSR - Overview: Electrolyte Panel, Serum — Mayo Clinic Laboratories, 2026 · Laboratory / reference-interval sourceAnion gap reference values from age 7: 7 to 15. The highest of the three intervals found.
- Anion Gap | MLabs — University of Michigan, Michigan Medicine Laboratories, 2026 · Laboratory / reference-interval sourceReference range 2 to 13 mmol/L, calculated as sodium minus chloride plus CO2, the same formula Sera uses.
- Anion Gap — North Bristol NHS Trust, Severn Pathology, 2026 · Laboratory / reference-interval sourceReference range 3 to 11 mmol/L; the page does not state the formula.
- Anion Gap Blood Test — MedlinePlus, U.S. National Library of Medicine, 2024 · Government / public-health guidanceGives no numeric normal range and states that normal results vary by laboratory.
What Anion Gap measures
Sodium minus the sum of chloride and bicarbonate, the conventional measure of unmeasured anions.
Calculated: Sodium − (Chloride + Bicarbonate), all mmol/L