Calculators · General Medicine · Formula

Anion gap, albumin-corrected anion gap and delta ratio

Also called AG, corrected anion gap, delta-delta, ΔAG/ΔHCO3

Serum anion gap with Figge albumin correction, plus the ΔAG/ΔHCO3 ratio for mixed disorders.

mmol/L
mmol/L
mmol/L

Figge correction uses the laboratory normal albumin.

mmol/L
mmol/L

Fill 3 more fields to see the result.

Formula and scoring

AG = Na − (Cl + HCO₃). Albumin-corrected AG = AG + 2.5 × (normal albumin − measured albumin) [g/dL] (0.25 per g/L). Delta ratio = (AG − normal AG) ÷ (normal HCO₃ − HCO₃).

Exam and ward pearls

  • Each 1 g/dL fall in albumin lowers the observed AG by about 2.5 mmol/L and can hide a lactic acidosis (Figge 1998).
  • A low AG suggests hypoalbuminaemia, lab error, paraproteinaemia (myeloma) or lithium/bromide toxicity.

When not to rely on it

  • Use your own laboratory reference values; the correction factor was derived in critically ill adults.

Source

  1. Figge J, Jabor A, Kazda A, Fencl V. Anion gap and hypoalbuminemia. Crit Care Med. 1998;26(11):1807-10. doi:10.1097/00003246-199811000-00019 · PMID 9824071
  2. Kraut JA, Madias NE. Serum anion gap: its uses and limitations in clinical medicine. Clin J Am Soc Nephrol. 2007;2(1):162-74. doi:10.2215/CJN.03020906 · PMID 17699401
  3. Rastegar A. Use of the ΔAG/ΔHCO3− ratio in the diagnosis of mixed acid-base disorders. J Am Soc Nephrol. 2007;18(9):2429-31. doi:10.1681/ASN.2006121408 · PMID 17656477

Formula and cut-offs checked against these sources on 8 Nov 2026. Educational tool for clinicians; it does not replace clinical judgement.

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