Calculator
Corrected Calcium Calculator
Adjusts total serum calcium for a patient's albumin level.
Corrected calcium
9.00mg/dL
Within the normal range of 8.5–10.2 mg/dL.
Patient values
The measured total calcium from the lab report.
Normal is 3.5–5.0 g/dL. Lower values need a bigger correction.
Try an example
Reference ranges
Corrected Ca = measured Ca + 0.8 × (4 − albumin in g/dL)
Roughly half of the calcium in blood is bound to albumin, and only the unbound (ionised) half is physiologically active. When albumin is low, the total calcium reported by the lab looks low even though the active calcium is normal. This formula estimates what the total would have been at a normal albumin of 4 g/dL.
It is an estimate, and it is least reliable in acidosis, alkalosis and dysproteinaemia. A measured ionised calcium remains the gold standard.
Common questions
4 g/dL is taken as a normal reference albumin. The formula asks what the total calcium would have been if the patient's albumin had been normal, so the further albumin sits below 4, the larger the correction added.
It is an empirical constant: each 1 g/dL fall in albumin lowers measured total calcium by roughly 0.8 mg/dL. It comes from population regression, which is exactly why the result is an estimate rather than a measurement.
Ionised calcium, whenever your lab can measure it. Corrected calcium is a bedside approximation for when it is unavailable; studies repeatedly show it misclassifies patients, particularly in renal failure and critical illness.
Yes. Switch the unit next to the field and the calculator converts to mg/dL before applying the formula. The result is always reported in mg/dL.
8.5–10.2 mg/dL for most adult laboratories. Below that is hypocalcaemia and above it hypercalcaemia — but always check the reference range printed on your own lab's report, as it varies slightly between assays.
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