Adjust total serum calcium for the patient's albumin level (Payne 1973).

What it is and when to use it

Albumin-corrected calcium estimates the total serum calcium a patient would have if their albumin were normal, because a substantial fraction of circulating calcium is bound to albumin. It is used in the setting of hypoalbuminemia (liver disease, nephrotic syndrome, critical illness, malnutrition), where measured total calcium underestimates true calcium and can mask hypo- or hypercalcemia. The classic Payne formula adds 0.8 mg/dL of calcium for every 1 g/dL of albumin below 4.0 g/dL (equivalent to +0.02 mmol/L for every 1 g/L below 40 g/L).

How to interpret it

The corrected value is interpreted against the usual total calcium reference range: normal is approximately 8.5-10.2 mg/dL (2.12-2.55 mmol/L). A corrected calcium below this range suggests hypocalcemia and above it hypercalcemia, even when the measured total calcium appears normal in the presence of low albumin. The correction does not change the diagnostic threshold, only the figure compared against it; for clinically relevant or discordant values, confirm with ionized calcium.

Limitations and when not to use it

The Payne correction was derived in specific populations and has limited reliability in advanced chronic kidney disease, pH disturbances (acidosis and alkalosis alter the ionized fraction), hyperphosphatemia, myeloma, or massive transfusion. It does not replace ionized calcium, which is the reference measure of the biologically active fraction and is preferred in the critically ill patient or when the clinical decision is critical. The result only adjusts for albumin and does not assess PTH, vitamin D, or the underlying cause of the calcium disorder.

Frequently asked questions

What is the formula for albumin-corrected calcium?

Corrected calcium (mg/dL) = measured total calcium + 0.8 × (4.0 − albumin in g/dL). In SI units: calcium (mmol/L) + 0.02 × (40 − albumin in g/L).

When should I use corrected calcium instead of total calcium?

When the patient has hypoalbuminemia, because measured total calcium underestimates true calcium and can hide a genuine hypo- or hypercalcemia.

Is ionized calcium more reliable than corrected calcium?

Yes. Ionized calcium directly measures the biologically active fraction and is the reference standard, especially in critically ill patients, pH disturbances, or advanced kidney disease.