About

Total serum calcium levels are tightly bound to albumin. In patients with hypoalbuminemia (low albumin), the total calcium measurement often falsely appears low, potentially leading to unnecessary treatment or misdiagnosis of hypocalcemia. Conversely, normal total calcium in the presence of low albumin may mask true hypercalcemia.

This tool applies the Payne formula to derive the "Corrected Calcium", providing a more accurate reflection of the physiologically active ionized calcium. This calculation is critical in oncology, nephrology, and intensive care settings where protein malnutrition or liver disease alters albumin synthesis. Accuracy here prevents iatrogenic errors in calcium replacement therapy.

Formulas

The calculator uses the standard Payne correction equation. Note that units must be standardized to mg/dL and g/dL before processing.

Ca_corrected = Ca_total + 0.8 × (4.0 − Alb_serum)

Where:

Ca_total is Total Serum Calcium (mg/dL)
Alb_serum is Serum Albumin (g/dL)
4.0 represents the normal mean albumin concentration.

Reference Data

Result State	Corrected Ca Range (mg/dL)	Corrected Ca Range (mmol/L)	Clinical Implication
Hypocalcemia	< 8.5	< 2.12	Tetany, seizures, arrhythmia
Normal	8.5 - 10.2	2.12 - 2.55	Physiologic homeostasis
Hypercalcemia	> 10.2	> 2.55	Stones, bones, groans, moans

Frequently Asked Questions

The formula is less accurate in patients with severe acidosis, alkalosis, or "paraproteinemia" (e.g., Multiple Myeloma). In these complex cases, direct measurement of Ionized Calcium (iCa) via blood gas analysis is the gold standard.

Yes, but the correction will be minimal. The formula is specifically designed to adjust for deviations from the albumin mean of 4.0 g/dL. If albumin is 4.0, corrected calcium equals total calcium.

For Calcium: Multiply mmol/L by 4.0 (approx) or exactly 4.008. For Albumin: Convert g/L to g/dL by dividing by 10.

Standard serum albumin ranges from 3.5 to 5.5 g/dL (35 to 55 g/L). Levels below 3.5 g/dL are considered hypoalbuminemia.