Adjust a measured serum calcium for low albumin, in both US and SI units.
How the corrected calcium calculator works
Roughly half of circulating calcium is bound to albumin, so a low albumin level makes total calcium read lower than the physiologically active ionised fraction. The correction adds back an estimate of that bound portion.
The correction is an approximation. Where the answer changes management, an ionised calcium measurement is the more reliable test.
A worked example
Take the starting scenario, a units of US — mg/dL calcium, g/dL albumin. That gives a corrected calcium of 9 mg/dL. Underneath, Measured calcium comes out at 8.2 mg/dL and Correction applied at 0.8 mg/dL. Change any field and every figure updates as you type.
Step by step
- Enter the measured total calcium.
- Enter serum albumin.
- Choose US or SI units and read the corrected value.
The calculation
US: corrected Ca = measured Ca + 0.8 × (4.0 − albumin g/dL)
SI: corrected Ca = measured Ca + 0.02 × (40 − albumin g/L)
FAQ
When is correction needed?
Whenever albumin is below the normal range — otherwise the measured calcium already reflects the true level closely.
Is corrected calcium reliable?
It is a reasonable approximation but can misclassify patients, particularly in critical illness or kidney disease. Ionised calcium is definitive.
What is the normal range?
Roughly 8.5–10.5 mg/dL, or 2.1–2.6 mmol/L, though laboratory ranges differ slightly.