How to Calculate Corrected Calcium
What is Corrected Calcium?
Low albumin falsely lowers measured serum calcium. Corrected calcium adjusts for this to reveal the true physiologically active level, essential for correct clinical interpretation.
Formula
Corrected Ca (mg/dL) = Measured Ca + 0.8 × (4.0 − Albumin (g/dL)); Accounts for low albumin falsely lowering measured calcium
- MeasuredCa
- Serum calcium measured (mg/dL (8.5–10.2 normal))
- Albumin
- Serum albumin (g/dL (3.5–5.5 normal))
- CorrectedCa
- Corrected serum calcium (mg/dL)
Step-by-Step Guide
- 1Corrected Ca = Measured Ca + 0.8 × (4 − Albumin g/dL)
- 2Normal albumin = 4 g/dL
- 3Normal corrected calcium = 8.5–10.5 mg/dL
- 4Each 1 g/dL drop in albumin lowers measured Ca ~0.8 mg/dL
Worked Examples
Input
Ca 7.6, Albumin 2.2 g/dL
Result
Corrected Ca = 7.6 + 0.8×1.8 = 9.04 mg/dL (actually normal)
Frequently Asked Questions
Why correct for albumin?
Albumin binds ~40% of serum calcium. Low albumin (malnutrition, liver disease, nephrotic syndrome) = low measured calcium but ionized calcium normal. Correction reveals true status.
When is corrected calcium clinically important?
Hypoalbuminemia common in chronic illness. Measured low calcium + normal albumin = probably normal. Correction prevents unnecessary calcium supplementation.
What if ionized calcium is available?
Ionized calcium best (biologically active form). Doesn't need correction. If available, use it. Correction formula useful when only total calcium available.
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