About 40% of calcium in the blood is bound to albumin. When albumin is low, total calcium falls even though the active, ionised calcium may be normal. Correction is an approximation. Ionised calcium is the definitive test, especially in critical illness.
How to use the Corrected Calcium Calculator
- Total calcium
- Albumin
- Normal albumin
Results update as you type, and every field accepts the units shown in its menu.
How it works
Enter total calcium and albumin from the same sample. You can change the normal albumin used in the formula.
Inputs explained
| Field | What to enter |
|---|---|
| Total calcium | Units: mg/dL, mmol/L |
| Albumin | Units: g/dL, g/L |
| Normal albumin | Units: g/dL, g/L |
Example values
How the main result changes when Total calcium changes and everything else stays at the example values above:
| Total calcium (mg/dL) | Corrected calcium (mg/dL) |
|---|---|
| 4 | 4.8 |
| 6 | 6.8 |
| 8 | 8.8 |
| 10 | 10.8 |
| 12 | 12.8 |
| 16 | 16.8 |
Health note: this calculator is for education and screening only and is not a diagnosis or treatment advice. Discuss your results with a qualified clinician.
Formula
Corrected Ca (mg/dL) = measured Ca + 0.8 × (4.0 − albumin g/dL)
(mmol/L: corrected = Ca + 0.02 × (40 − albumin g/L))
Worked example
Inputs: Total calcium: 8 mg/dL; Albumin: 3 g/dL; Normal albumin: 4 g/dL.
Results: Corrected calcium = 8.8 mg/dL.
Key terms
- Ionised calcium
- The free, active form of calcium.
Frequently asked questions
What is a normal calcium?
About 8.5–10.5 mg/dL (2.12–2.62 mmol/L).
When should ionised calcium be measured?
In critical illness, kidney failure, abnormal pH and when results do not fit.
Why might corrected calcium be wrong?
The formula is an approximation and performs poorly in some patients.