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Corrected Calcium Calculator
Total blood calcium looks falsely low when albumin is low, because much of the calcium rides on albumin. This calculator applies the standard correction: corrected calcium = measured calcium + 0.8 × (4.0 − albumin). Educational use only — not medical advice.
The formula
Corrected calcium (mg/dL) = measured total calcium (mg/dL) + 0.8 × (4.0 − albumin in g/dL). Example: calcium 8.0 with albumin 2.5 gives 8.0 + 0.8 × 1.5 = 9.2 mg/dL — back inside the normal range, which changes the clinical picture entirely.
When it applies — and when it does not
The formula is a bedside estimate for low albumin. It is unreliable in kidney failure, myeloma, and acid-base disorders, and it never replaces ionized (free) calcium measurement, which is the definitive test. If the result worries you, discuss it with a clinician — do not self-diagnose from a calculator.
Frequently Asked Questions
Why correct calcium at all?
About half of blood calcium is bound to albumin. Low albumin lowers total calcium without lowering the active (ionized) fraction — the correction estimates what total calcium would be at normal albumin.
What units does it use?
mg/dL for calcium and g/dL for albumin, the standard US units. If your lab reports mmol/L, convert first (calcium mmol/L × 4 = mg/dL approx).
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