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Corrected calcium for albumin

Total (not ionized) serum calcium. Accepts mg/dL or mmol/L.

Serum albumin. 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

Corrected calcium (mg/dL) = measured total calcium + 0.8 × (4.0 − serum albumin in g/dL). In SI units: corrected calcium (mmol/L) = measured + 0.02 × (40 − albumin in g/L). 4.0 g/dL (40 g/L) is the reference-normal albumin at which no correction is applied; below it the correction raises an artefactually low total calcium, above it it lowers it. The 0.8 (0.02) coefficient is the widely used rounded form of Payne's original 1.0 (0.025) slope.

Limitations and notes

No interpretation bands: the output is a transformed lab value read against the ordinary total-calcium reference range, which is age-specific in children (Roizen 2013, PMID 24217904). Do not attach an automated normal/abnormal verdict. Headline caveat: the correction is unreliable in critical illness and does not track ionized calcium well (Steele 2013: adjusted Ca <2.2 mmol/L had only 78% sensitivity / 63% specificity, AUC 0.78 for ionized hypocalcemia) — direct ionized calcium is the reference standard in the critically ill, acid-base disturbance, after citrate-containing transfusion, or with rapid albumin shifts. The albumin–calcium binding constant is not fixed, so a fixed linear coefficient overestimates ionized calcium at low albumin. The 0.8 (0.02) coefficient is a rounded convention of Payne's printed 1.0 (0.025) slope: for Ca 7.6 mg/dL / albumin 2.0 g/dL the two forms differ by 0.4 mg/dL (9.2 vs 9.6). The slope is assay- and population-specific (bromocresol green vs purple albumin methods differ; locally validated equations are recommended), and the reference albumin (4.0 g/dL) may be replaced by a local mean normal albumin. Payne's derivation cohort was 200 adults with no ionized-calcium validation — there is no pediatric-specific derivation, so applying it to neonates/unstable children is an extrapolation (prefer ionized calcium). [NEEDS SOURCE] for a fetched pediatric albumin reference interval, a fetched primary pediatric ionized-calcium interval, and the reported (unverified) low sensitivity in trauma.

Accepted input ranges

  • Measured total calcium — 4–20 mg/dL
  • Serum albumin — 1–6 g/dL

References

  1. Payne RB, Little AJ, Williams RB, Milner JR. Interpretation of serum calcium in patients with abnormal serum proteins. Br Med J. 1973;4(5893):643–646.PMID 4758544DOI 10.1136/bmj.4.5893.643
  2. Steele T, Kolamunnage-Dona R, Downey C, Toh CH, Welters I. Albumin-adjusted calcium concentration should not be used to identify hypocalcaemia in critical illness. Crit Care. 2013;17(Suppl 2):P446.DOI 10.1186/cc12384
  3. Roizen JD, Shah V, Levine MA, Carlow DC. Determination of Reference Intervals for Serum Total Calcium in the Vitamin D-Replete Pediatric Population. J Clin Endocrinol Metab. 2013;98(12):E1946–E1950.PMID 24217904DOI 10.1210/jc.2013-3105

Version and changelog

v1.0.0 · Renal and metabolic

  • 2026-07-25 v1.0.0 — Initial release: albumin-corrected calcium (Payne, de-facto 0.8/0.02 coefficient); no bands.

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.