Blood tests and kidneys
Anion gap
Anion gap, with or without potassium, and corrected for a low albumin.
For education. Check against your unit's guidance and a second clinician before use.
mmol/L
mmol/L
mmol/L
Optional. Some labs include it; the normal range is then higher.
mmol/L
Optional. A low albumin hides a raised anion gap.
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Before you use this
- Normal ranges depend on the lab's analyser. Without potassium, about 8–16 mmol/L is often quoted; check your lab's range.
- A raised anion gap metabolic acidosis suggests unmeasured acids: ketones (DKA), lactate, kidney failure, or poisoning (for example methanol, ethylene glycol, salicylate).
How this is calculated
- Anion gap = sodium − (chloride + bicarbonate)
- With potassium: (sodium + potassium) − (chloride + bicarbonate)
- Corrected for albumin = anion gap + 0.25 × (40 − albumin in g/L)
Sources
- Kraut JA, Madias NE. Serum anion gap: its uses and limitations in clinical medicine. Clin J Am Soc Nephrol 2007;2:162–74.
- Figge J, Jabor A, Kazda A, Fencl V. Anion gap and hypoalbuminemia. Crit Care Med 1998;26:1807–10.
Checked by PICUlearn, 21 Sept 2026.