Anion Gap
Enter sodium, chloride and bicarbonate to see the gap.
Notes
Hypoalbuminaemia hides a gap. Albumin is the largest unmeasured anion, so a low albumin drags the calculated gap down and can make a real gap acidosis look normal. That is the point of the adjustment, and it matters most in exactly the sick patients whose gap is being checked.
The reference albumin is 40g/L here. Figge writes the correction against “[normal albumin]” without fixing a value, which is why other calculators quote 4.0, 4.4 or 4.5 g/dL — each has quietly chosen one. Use your own laboratory's normal if it differs.
The delta ratio bands are conventional teaching, not part of the source paper. Treat a ratio outside 1–2 as a prompt to look for a second acid–base disorder, not as a diagnosis.
The ratio needs a metabolic acidosis to mean anything, so it appears only when the bicarbonate is below 24 — above that its denominator is zero or negative.
Show formula
Anion gap = Na⁺ − (Cl⁻ + HCO₃⁻)
Adjusted for albumin = gap + 0.25 × (normal albumin − measured), in g/L
Delta ratio = (gap − 12) ÷ (24 − HCO₃⁻)