Corrected Calcium Calculator

Roughly 40% of the calcium circulating in blood is bound to albumin, so total serum calcium reads artificially low in patients with hypoalbuminemia even when the physiologically active, unbound (ionized) fraction is perfectly normal. This calculator applies the standard correction, corrected calcium = measured calcium + 0.8 x (4.0 - albumin), published by Payne and colleagues in the British Medical Journal in 1973, which adds back an estimated 0.8 mg/dL of calcium for every 1 g/dL the patient's albumin sits below the reference value of 4.0 g/dL -- and subtracts the same amount if albumin runs above 4.0. Raising Measured Calcium always raises Corrected Calcium one-for-one, since the formula simply adds a separate correction term on top of it; raising Albumin always lowers Corrected Calcium, since a higher albumin means less of a downward correction is needed.

That correction term, labeled Correction Amount, depends only on Albumin and is completely unaffected by whatever the Measured Calcium value happens to be -- the two halves of the formula are independent. The corrected result is then classified against the normal total calcium range of 8.5-10.5 mg/dL. This formula corrects for albumin only; it does not account for acid-base disturbances, which also shift the ionized fraction, so a directly measured ionized calcium remains the more reliable test when it's available and the clinical picture is ambiguous.