How the Corrected Calcium Calculator works
About 40% of calcium in the blood is bound to albumin. When albumin is low, total calcium falls even if the physiologically active ionized calcium is normal. "Corrected" calcium is an estimate of what the total calcium would be if albumin were normal.
This calculator uses one formula only — the Payne (1973) adjustment with a reference albumin of 4.0 g/dL — so results are consistent and traceable.
Required inputs
- Measured total calcium in mg/dL or mmol/L (mmol/L × 4.008 = mg/dL)
- Serum albumin in g/dL or g/L (g/L ÷ 10 = g/dL)
Formula used
Equivalent in SI units: corrected Ca (mmol/L) = Ca (mmol/L) + 0.02 × [40 − albumin (g/L)].
Worked example
Measured calcium 8.0 mg/dL and albumin 3.0 g/dL:
- Corrected calcium = 8.0 + 0.8 × (4.0 − 3.0) = 8.8 mg/dL (≈ 2.20 mmol/L)
Interpreting the result
A commonly cited adult reference interval for total calcium is about 8.5–10.2 mg/dL (2.13–2.55 mmol/L), but intervals vary between laboratories. A corrected value outside the interval may need further evaluation — often with a directly measured ionized calcium.
Limitations
- Corrected calcium is not equivalent to measured ionized calcium, which is the preferred test when accuracy matters.
- Studies show albumin-correction formulas can misclassify calcium status, particularly in critical illness, chronic kidney disease, and acid–base disturbances.
- Some laboratories use locally derived correction formulas — results may differ from this calculator.
- Do not mix units: enter calcium and albumin exactly as reported and select the matching units.