Corrected Calcium Calculator

Roughly 40 percent of the calcium in blood is bound to albumin, so a low albumin makes measured total calcium read low while the active fraction is unchanged. This applies the Payne formula, corrected calcium = measured calcium + 0.8 x (4.0 - albumin), with calcium in mg/dL and albumin in g/dL, alongside an SI mode in mmol/L and g/L. It is an approximation published in 1973 and it agrees poorly with measured ionised calcium in critical illness, renal disease and acid-base disturbance. Ionised calcium is the actual measurement, and the result belongs with the clinician who ordered the test.