Corrected Calcium

What This Calculator Measures

Adjusts measured total serum calcium for hypoalbuminemia to estimate the physiologically relevant total calcium, since a large fraction of serum calcium is albumin-bound.

How to Use

1. Measure total serum calcium (mg/dL) and albumin (g/dL) from the same blood sample.
2. Enter both values.
3. Review the corrected calcium against the normal range.
4. When ionized calcium is available, use it for clinical decisions, especially in the critically ill.

Interpretation Guide

Corrected calcium < 8.5 mg/dL indicates hypocalcemia, 8.5–10.5 mg/dL is normal, ≥ 10.6 mg/dL is hypercalcemia, and ≥ 12.5 mg/dL is severe hypercalcemia. The correction assumes a normal albumin of 4.0 g/dL and becomes less reliable when albumin is below 2.0 g/dL. In neonates and children, correction factors and reference ranges differ.

Clinical Significance

Because a large fraction of serum calcium is protein-bound, low albumin can mask true calcium status; correction helps avoid unnecessary treatment of spurious hypocalcemia.

When to Use

• Interpreting total calcium when serum albumin is low (liver disease, nephrotic syndrome, malnutrition)
• Initial assessment for possible hypocalcemia or hypercalcemia
• When ionized calcium measurement is unavailable

When Not to Use

• In critically ill patients, where ionized calcium is preferred
• When hypercalcemia is suspected — the correction is not validated for that setting
• In neonates and children, where reference ranges and correction factors differ
• In patients with marked acid-base disturbance, which alters calcium–albumin binding

Limitations

• Assumes a fixed relationship between albumin and calcium binding that varies across populations.
• Does not account for serum pH, which changes calcium–protein binding.
• Becomes less reliable when albumin is below 2.0 g/dL.
• Is not a substitute for ionized calcium measurement.
• The 0.8 correction factor is an estimate; some institutions use 0.7 or 0.73.

Worked Example

A 63-year-old woman with cirrhosis has a measured total calcium of 8.0 mg/dL and serum albumin of 2.0 g/dL.

Corrected calcium = 8.0 + 0.8 × (4 − 2) = 9.6 mg/dL, within the normal range. The low measured calcium was explained by hypoalbuminemia.

Evidence

Source

Clinical Biochemistry

Reference

Payne RB, et al. Interpretation of serum calcium in patients with abnormal serum proteins. Br Med J. 1973;4(5893):643-646.

Reviewed By

MedCalcHub Clinical Team

Version

1.0

Updated

2026-08

1. Payne RB, et al. Br Med J. 1973;4(5893):643-646.

References

1. Payne RB, et al. Interpretation of serum calcium in patients with abnormal serum proteins. Br Med J. 1973;4(5893):643-646. (Original Description)

Frequently Asked Questions