Corrected calcium (Payne formula)
About 40% of serum calcium is bound to proteins, mainly albumin. When albumin is low, total calcium falls without free calcium necessarily falling. The Payne formula adjusts total calcium to an albumin of 4.0 g/dl (40 g/l).
⚠︎ Learning tool for medical education – not for use in patients or for treatment decisions.
Formula
Payne et al. (1973): adjusted calcium (mg/dl) = calcium (mg/dl) − albumin (g/dl) + 4.0. In SI units this corresponds approximately to adjusted calcium (mmol/l) = calcium (mmol/l) + 0.025 × (40 − albumin in g/l). Conversion: 1 mmol/l calcium = 4.008 mg/dl.
Payne et al. derived the formula from the regression of calcium on albumin in 200 specimens sent for liver function tests. After adjustment, the 95% limits matched the normal range of their laboratory.
Limitations
Ladenson et al. (1978) compared 13 published correction formulas with measured free (ionised) calcium: none predicted calcium status substantially better than uncorrected total calcium. The formula also depends on the laboratory’s albumin method; reference ranges are laboratory-specific and are not shown here.
FAQ
What does adjusted calcium indicate?▾
The adjustment estimates what total calcium would be at a normal albumin. Direct measurement of free calcium gives the most accurate information about it.
Why are there different correction formulas?▾
The formulas are based on regressions in individual laboratories and depend on their measurement methods. Ladenson et al. (1978) tested 13 different published formulas.
References
- Payne RB, Little AJ, Williams RB, Milner JR. Interpretation of serum calcium in patients with abnormal serum proteins. Br Med J 1973;4:643–6. · PubMed
- Ladenson JH, Lewis JW, Boyd JC. Failure of total calcium corrected for protein, albumin, and pH to correctly assess free calcium status. J Clin Endocrinol Metab 1978;46:986–93. · PubMed
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Open in browser Download on the App StoreIntended purpose: learning tool for medical education only. Not intended for use in patients or for diagnostic or treatment decisions; not a medical device. Calculations follow the cited original publications; no guarantee of completeness or correctness. Last updated: 10/2026 · Dr. Pascal Bafteh