Corrected Calcium Calculator (Albumin-Adjusted Calcium)
Adjust total serum calcium for low albumin to estimate the physiologically active level.
✓ Formulas cited from the published literature
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About this calculator
About 40–45% of blood calcium is bound to albumin. When albumin is low, total calcium reads low even though the free, active (ionised) calcium may be normal. The corrected calcium formula estimates what total calcium would be if albumin were normal.
How it works
Corrected Ca (mg/dL) = measured Ca + 0.8 × (4.0 − albumin in g/dL)
SI version: Corrected Ca (mmol/L) = measured Ca + 0.02 × (40 − albumin in g/L). Unit conversion: mg/dL ÷ 4.008 = mmol/L.
How to read your result
If corrected calcium is outside 8.5–10.5 mg/dL, confirm with an ionised calcium measurement before acting, especially in ICU, renal and acid-base disturbances where the correction performs poorly.
Worked example
Total calcium 8.2 mg/dL with albumin 2.5 g/dL.
| Corrected calcium | 9.4 mg/dL Within the usual range (8.5–10.5 mg/dL) |
| In SI units | 2.35 mmol/L Usual range 2.12–2.62 mmol/L |
Frequently asked questions
Why correct calcium for albumin?
Because albumin binds calcium, low albumin lowers total calcium without lowering active calcium, which can lead to unnecessary treatment.
Is corrected calcium accurate?
It is an approximation. Studies show it misclassifies a notable share of patients, so ionised calcium is preferred when it matters.
What is the normal calcium range?
Roughly 8.5–10.5 mg/dL (2.12–2.62 mmol/L). Laboratory ranges vary slightly.
Limitations and when not to use
Not validated in critical illness, dialysis, pregnancy or with extreme albumin values.
Sources and references
- Payne RB, et al. Interpretation of serum calcium in patients with abnormal serum proteins. BMJ 1973;4:643–646.
Last updated: 2026-10-09