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Corrected Calcium Calculator

Adjust a measured total calcium reading for a low albumin level: corrected Ca = measured Ca + 0.8 × (4.0 − albumin).

Corrected calcium (mg/dL)
9.4 mg/dL
Corrected calcium (mmol/L)
2.35 mmol/L
Correction applied
+1.6 mg/dL
Where this falls
Normal range

How it works

Roughly 40% of total blood calcium is bound to albumin, so when albumin is low (hypoalbuminemia), total calcium reads lower than the physiologically active, unbound (ionized) calcium that's actually available in the body — the measurement looks low even though nothing is actually wrong with calcium regulation. The Payne correction (Payne et al., 1973) adjusts for this: corrected calcium (mg/dL) = measured calcium (mg/dL) + 0.8 × (4.0 − albumin (g/dL)), using 4.0 g/dL as the reference albumin level.

At an albumin of exactly 4.0 g/dL, the correction is zero and the corrected value equals the measured value. Below 4.0 g/dL, the formula adds to the measured reading; above 4.0 g/dL, it subtracts — though the formula is most commonly applied, and most validated, specifically for correcting low albumin, not high albumin. The mg/dL result is also converted to mmol/L by multiplying by 0.2495, the standard calcium unit conversion factor.

FAQ

When is this correction actually used?

Mainly when albumin is below its normal range (roughly under 3.5-4 g/dL) — common in malnutrition, liver disease, nephrotic syndrome, or critical illness — since that's when raw total calcium is most likely to understate true calcium status. When albumin is in its normal range, the correction changes the result very little and raw total calcium is usually sufficient.

Is the corrected value as reliable as a direct ionized calcium test?

No — it's a widely used estimate, not a replacement for direct ionized calcium measurement when that's available and precision matters (e.g. in critically ill patients). It's most useful as a quick adjustment when only total calcium and albumin are on hand.

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