Clinical Calculators

Anion Gap (AG)

Na − (Cl + HCO3⁻). Also gives an albumin-corrected anion gap when albumin is low

AG 3 items left
Corrected AG (albumin-corrected) 5 items left

120 to 160
mEq/L
80 to 130
mEq/L
10 to 40
mEq/L
1.5 to 5.5
g/dL

Enter only to get the corrected AG. The AG is shown even if this is left blank

3.5 to 5
g/dL

Enter only to get the corrected AG. Use the reference albumin value your institution (laboratory) uses

Formula

  • AG (mEq/L) = Na − (Cl + HCO3⁻)
  • Corrected AG (mEq/L) = AG + 2.5 × (reference albumin − measured albumin). The factor is 2.5 for albumin in g/dL (0.25 for g/L). Each 1 g/dL fall in albumin lowers the measured AG by 2.3 to 2.5 mEq/L

Cautions

  • The reference range of the AG differs between laboratories and methods (textbooks give 8 to 16, 7 to 13, 3 to 11 and others; it is lower with ion-selective electrodes). The normal range itself is 8 to 10 mEq/L wide, so compare the result with your own laboratory's reference range (Kraut 2013). This tool does not label a result normal or abnormal.
  • An AG calculated with K included is a different formula with a different reference range. This tool uses the formula without K (the one in most US textbooks).
  • When albumin is low, the AG reads falsely low, and a high-AG metabolic acidosis can be missed. The corrected AG uses the formula of Figge et al. (1998), 2.5 mEq/L for each 1 g/dL of albumin. Enter your institution's reference albumin value.
  • The correction factor also changes with pH, which alters the charge on albumin (Kraut 2013). Treat the corrected AG as a rough guide.
  • This tool's sources do not give a reference range for children or newborns. When using it in a child, check your institution's reference range.

References

  1. Kraut JA, Nagami GT. The serum anion gap in the evaluation of acid-base disorders: what are its limitations and can its effectiveness be improved? Clin J Am Soc Nephrol. 2013;8(11):2018-2024. (Definition and Characterization of the Normal Serum Anion Gap; Table 1) DOI: 10.2215/CJN.04040413[Review article]
  2. Figge J, Jabor A, Kazda A, Fencl V. Anion gap and hypoalbuminemia. Crit Care Med. 1998;26(11):1807-1810. (Abstract) (original not seen) PMID: 9824071, DOI: 10.1097/00003246-199811000-00019[Original article]
  3. Kraut JA, Madias NE. Serum anion gap: its uses and limitations in clinical medicine. Clin J Am Soc Nephrol. 2007;2(1):162-174. (Abstract) (original not seen) PMID: 17699401, DOI: 10.2215/CJN.03020906[Review article]

Checked on: 2026-10-13

Disclaimer

This calculation is intended to support the judgment of healthcare professionals. Results are for reference only; decisions about diagnosis and treatment must be made by the responsible healthcare professional. The values you enter never leave your device.