How to use it
- Enter sodium, chloride and bicarbonate (total CO₂) from the same blood sample, in mEq/L or mmol/L.
- Optionally turn on potassium and enter it.
- Optionally turn on albumin correction, choose g/dL or g/L and enter the albumin.
- Read the anion gap and, if chosen, the albumin-corrected gap.
Formulas
- Anion gap = Na⁺ − (Cl⁻ + HCO₃⁻)
- With potassium = Na⁺ + K⁺ − (Cl⁻ + HCO₃⁻)
- Albumin-corrected gap = anion gap + 2.5 × (4.0 − albumin in g/dL)
Albumin in g/L is divided by 10 first, which is the same as adding 0.25 × (40 − albumin in g/L). When potassium is included, the corrected gap is built on the gap with potassium.
Worked example
Sodium 135, chloride 100, bicarbonate 15 mEq/L, albumin 2.0 g/dL:
- Anion gap = 135 − (100 + 15) = 20 mEq/L
- Corrected = 20 + 2.5 × (4.0 − 2.0) = 25 mEq/L
With normal values, 140 − (104 + 24) = 12 mEq/L; adding potassium 4.0 gives 16 mEq/L.
Tips and common mistakes
- Use values from one sample; mixing results from different times gives a meaningless gap.
- Compare the gap only with a reference range calculated the same way (with or without potassium).
- High albumin, above 4.0 g/dL, lowers the corrected gap.
- This is an estimate for information, not a diagnosis. Acid–base problems need a clinician’s assessment.