Why is albumin correction needed for calcium?

About 40–45% of serum calcium is protein-bound, mainly to albumin. In hypoalbuminemia, total measured calcium is falsely low even if ionized (physiologically active) calcium is normal. The Payne formula estimates what total calcium would be if albumin were 4.0 g/dL.

What is the Payne formula?

Corrected Ca (mg/dL) = Measured Ca (mg/dL) + 0.8 × (4.0 − Albumin g/dL). For mmol/L units the constant is 0.02 × (40 − Albumin g/L).

What are normal corrected calcium ranges?

Normal serum calcium is approximately 8.5–10.5 mg/dL (2.12–2.62 mmol/L). Values below 8.5 mg/dL suggest hypocalcemia; values above 10.5 mg/dL suggest hypercalcemia.

When should I measure ionized calcium instead?

Ionized calcium is more accurate in critically ill patients, those with acid-base disturbances, multiple myeloma, or when albumin correction gives borderline results. Use ionized calcium when clinical uncertainty remains.

Does this tool provide medical advice?

No. This calculator is for educational and informational purposes only. Always interpret results in clinical context and consult a qualified clinician for patient care decisions.

Calcium Correction for Albumin Calculator

Enter measured serum calcium and albumin to get the corrected calcium using the Payne formula.

Patient Values

Unit System

Measured Serum Calcium

mg/dL

Serum Albumin

g/dL

Payne formula (mg/dL):
Corrected Ca = Measured Ca + 0.8 × (4.0 − Albumin)

Result

Enter values and click Calculate

Summary

This calculator applies the Payne formula to correct total serum calcium for a low albumin level. Because roughly 40% of serum calcium is albumin-bound, a low albumin artificially lowers total calcium measurements. Enter your measured calcium and albumin values in mg/dL (or mmol/L) to see the corrected calcium and a brief clinical interpretation.

How it works

Enter your measured serum calcium (mg/dL or mmol/L).
Enter the serum albumin level (g/dL or g/L).
The Payne formula is applied: Corrected Ca = Measured Ca + 0.8 × (4.0 − Albumin).
The corrected calcium and interpretation are displayed instantly.
Switch between mg/dL and mmol/L unit systems before calculating.

Use cases

Evaluating true calcium status in hypoalbuminemic patients.
Screening for hypercalcemia or hypocalcemia masked by low albumin.
Adjusting calcium interpretation in critically ill or malnourished patients.
Clinical decision support before ordering ionized calcium tests.
Teaching tool for medical students learning electrolyte correction.

Frequently Asked Questions

Last updated: 2026-06-11 · Reviewed by Nham Vu