Adjust total serum calcium for a low albumin level using the Payne formula. Enter measured calcium (mg/dL) and serum albumin (g/dL).
Formula: corrected Ca (mg/dL) = measured Ca + 0.8 x (4.0 - albumin). Normal albumin reference is 4.0 g/dL.
This estimate uses the Payne albumin correction. It is not the same as a directly measured ionized calcium. Interpret alongside clinical findings.
When serum albumin is low, total calcium measured in the lab will read lower than expected because less albumin is available to bind calcium. The Payne formula estimates what total calcium would be if albumin were at the standard reference value of 4.0 g/dL.
For example: measured calcium 8.0 mg/dL, albumin 2.5 g/dL. Corrected Ca = 8.0 + 0.8 x (4.0 - 2.5) = 8.0 + 0.8 x 1.5 = 8.0 + 1.2 = 9.2 mg/dL.
The Payne formula is a linear approximation. Studies have shown it can be inaccurate in critically ill patients, in those with acid-base disturbances, and at extreme albumin values. Many clinicians prefer to order direct ionized calcium measurement in those situations because it measures the physiologically active fraction without relying on a correction factor.
The formula was published by Payne RB, Little AJ, Williams RB, Milner JR. "Interpretation of serum calcium in patients with abnormal serum proteins." British Medical Journal, 1973;4(5893):643-646. See also the MDCalc calcium correction reference for further discussion of variants.
Kidney disease frequently lowers albumin and alters calcium metabolism. See the GFR Calculator (CKD-EPI 2021) for kidney function estimation, and the Creatinine Clearance Calculator for drug dosing context.
The Payne formula is: corrected calcium (mg/dL) = measured calcium (mg/dL) + 0.8 x (4.0 - serum albumin in g/dL). It adjusts the measured total calcium for a below-normal albumin level. Published by Payne RB and colleagues in the British Medical Journal, 1973.
About 40 to 45 percent of calcium in blood is bound to albumin. When albumin is low, total calcium measured by the lab appears lower than the physiologically active (ionized) fraction would suggest. The correction formula estimates what the total calcium would be at a normal albumin of 4.0 g/dL.
The typical reference range for total serum calcium is 8.5 to 10.5 mg/dL, though this varies by laboratory. The corrected calcium formula is an estimate and has known limitations. A healthcare provider interprets the result alongside clinical symptoms and other tests, including direct ionized calcium measurement.
No. Ionized calcium is measured directly and reflects the biologically active fraction. Corrected calcium is an algebraic estimate from total calcium and albumin. Direct ionized calcium measurement is more accurate, particularly in critically ill patients or those with acid-base disorders.