How to use this calculator
- Enter or choose sodium (Na⁺).
- Enter or choose potassium (K⁺).
- Enter or choose chloride (Cl⁻).
- Enter or choose bicarbonate (HCO₃⁻).
- Enter or choose albumin in.
- The anion gap updates as you type. Use Copy result or Share to keep it.
Method
AG = Na⁺ − (Cl⁻ + HCO₃⁻); AG with K = (Na⁺ + K⁺) − (Cl⁻ + HCO₃⁻); Corrected AG = AG + 2.5 × (Reference albumin − Albumin, g/dL)
- Na⁺, K⁺, Cl⁻, HCO₃⁻
- serum electrolytes in mmol/L (equal to mEq/L for these ions)
- Albumin
- serum albumin; g/L ÷ 10 = g/dL
- 2.5
- mmol/L added per 1 g/dL fall in albumin
Worked example
- AG = 140 − (104 + 24) = 12 mmol/L.
- Including potassium: 12 + 4 = 16 mmol/L.
- Albumin correction: 12 + 2.5 × (4.0 − 2.0) = 17 mmol/L.
With Na 140, Cl 104 and HCO₃ 24 the anion gap is 12 mmol/L, which corrects to 17 mmol/L for an albumin of 2.0 g/dL.
What the result means
Compare the gap with the reference range of the laboratory that ran the test, since ranges depend on the analyser and on whether potassium is included. Low albumin hides a raised gap, which is why the corrected value is shown.
Assumptions and limits
- All electrolytes come from the same sample and are in mmol/L.
- The albumin correction uses 2.5 mmol/L per g/dL, the commonly quoted factor.
- Reference ranges differ between laboratories; no cut-off is applied here.
- Other unmeasured ions (for example paraproteins, lithium, bromide) can distort the gap.
Questions
Should potassium be included?
Most laboratories now leave it out, but some include it. Both values are shown; compare with the range for the method your laboratory uses.
Why correct for albumin?
Albumin is the main unmeasured anion. When it is low, the gap falls, which can mask an added acid; the correction adds about 2.5 mmol/L per g/dL of missing albumin.
Sources
Please note: This is a general screening estimate for adults, not medical advice or a diagnosis. Talk to a qualified health professional about your health.