Skip to content
TowardPCC
All calculators

Anion gap (with albumin correction)

From the electrolyte panel. Accepts mEq/L or mmol/L (identical).

From the electrolyte panel. Accepts mEq/L or mmol/L (identical).

Bicarbonate or the total CO₂ reported on a basic metabolic panel (used interchangeably here). Accepts mEq/L or mmol/L (identical).

Optional. Supply only to also compute the potassium-inclusive AG, which uses a higher reference interval.

Optional. Supply to also compute the albumin-corrected AG (baseline 4.0 g/dL). Accepts g/dL or g/L.

Independent clinical validation: pending

Two independent clinical validators will be named here once review is complete.

Validator slot open 1
Validator slot open 2

How it is calculated

Base anion gap = sodium − (chloride + bicarbonate). When potassium is supplied, the potassium-inclusive anion gap = (sodium + potassium) − (chloride + bicarbonate); it runs about 3.5–5 units higher and uses a higher reference interval, so the two forms are shown separately. When albumin is supplied, the albumin-corrected anion gap = anion gap + 2.5 × (4.0 − albumin in g/dL): each 1 g/dL of albumin below the 4.0 g/dL baseline adds 2.5 mEq/L back to the gap (Figge 1998), unmasking a high-anion-gap acidosis that hypoalbuminemia would otherwise hide. Values are reported in mEq/L (numerically equal to mmol/L for these monovalent ions).

Limitations and notes

The anion gap is a diagnostic/classification index, not a graded severity or outcome score — do not read it as a mortality or acuity score. It has NO interpretation bands here because reference intervals are strongly method-dependent (flame photometry gave ~12 ± 4 mEq/L; modern ion-selective electrodes shifted it down to ~6 ± 3, and verified lab intervals range widely, e.g. 10–18 mmol/L K-exclusive in Chionh 2022): always classify against the reporting lab's own reference interval, not a fixed cutoff. The potassium-inclusive form runs ~3.5–5 units higher and requires a correspondingly higher reference interval — never compare a K-inclusive value against a K-exclusive range. The albumin correction uses the Figge 1998 slope of 2.5 mEq/L per 1 g/dL below a 4.0 g/dL baseline (equivalently 0.25 per g/L below 40 g/L); a small number of sources use a 2.3 coefficient or a 4.5 g/dL baseline (results are clinically near-identical) — this implementation uses 2.5 and 4.0, the most common clinical form. Correcting for albumin increases sensitivity, not specificity, and is an adjunct to — not a replacement for — direct measurement of lactate, ketones, etc. Pediatric-first flag: the 2.5 coefficient and the reference intervals were derived predominantly in ADULTS (Figge's cohort was adults); they are applied to children by convention, not from pediatric-derived data. Total CO₂ from a basic metabolic panel is used interchangeably with HCO₃ (a ~1–2 mmol/L offset, conventionally ignored). [NEEDS SOURCE]: the na (100–180), cl (70–130), hco3 (3–45), k (1.5–9) mEq/L and albumin (1.0–6.0 g/dL) input limits are engineering input-validity bounds, not thresholds from a specific publication. Garbage-in caveat: spurious electrolyte values (pseudohyponatremia, bromide interference with the chloride assay) distort the AG directly.

Accepted input ranges

  • Serum sodium (Na⁺) — 100–180 mEq/L
  • Serum chloride (Cl⁻) — 70–130 mEq/L
  • Serum bicarbonate (HCO₃⁻ or total CO₂) — 3–45 mEq/L
  • Serum potassium (K⁺, optional) — 1.5–9 mEq/L
  • Serum albumin (optional) — 1–6 g/dL

References

  1. Figge J, Jabor A, Kazda A, Fencl V. Anion gap and hypoalbuminemia. Crit Care Med. 1998;26(11):1807–1810.PMID 9824071DOI 10.1097/00003246-199811000-00019
  2. Kraut JA, Madias NE. Serum anion gap: its uses and limitations in clinical medicine. Clin J Am Soc Nephrol. 2007;2(1):162–174.PMID 17699401DOI 10.2215/CJN.03020906
  3. Chionh CY, Poh CB, Roy DM, et al. Serum anion gap revisited: a verified reference interval for contemporary use. Intern Med J. 2022;52(9):1531–1537.PMID 34028972DOI 10.1111/imj.15396
  4. Anion Gap and Non–Anion Gap Metabolic Acidosis. StatPearls (NCBI Bookshelf), NBK448090.Source

Version and changelog

v1.0.0 · Renal and metabolic

  • 2026-07-25 v1.0.0 — Initial release: anion gap (K-exclusive and K-inclusive) with the Figge 1998 albumin correction.

Important

For use by qualified health professionals as an informational and educational aid. It supports clinical judgment and does not replace it. Verify every result independently before making a clinical decision. This is not a medical device.