Albumin-Corrected Calcium (Payne)

Formula

Corrected Ca (mg/dL) = measured Ca + 0.8 x (4.0 - albumin g/dL).

Limitations

• Unreliable in critical illness, acid-base disturbances, chronic kidney disease and at extremes of albumin; ionised calcium is the reference measurement.
• The reference interval used here, 8.8 to 10.4 mg/dL (2.20 to 2.60 mmol/L), is the one given by the MSD Manual; laboratory intervals differ.
• Versions of the correction differ: this tool uses the widely quoted factor of 0.8 mg/dL per g/dL of albumin below 4.0 g/dL (0.02 mmol/L per g/L below 40 g/L), whereas the abstract of Payne's 1973 paper gives the simpler adjustment 'calcium - albumin + 4.0' (a factor of 1.0); the two differ by a few tenths of mg/dL at low albumin.

References

1. Interpretation of serum calcium in patients with abnormal serum proteins. Payne RB, Little AJ, Williams RB, Milner JR. Br Med J. 1973;4(5893):643-646. PMID 4758544