Corrected Calcium

Roughly 40% of serum calcium is albumin-bound, so hypoalbuminaemia lowers total calcium without changing the physiologically active ionised fraction. Correction estimates what the total would be at a normal albumin of 40 g/L. It is an approximation and performs poorly in critical illness, renal failure and acid-base disturbance — where the correction is least reliable is exactly where it is most often applied. Measure ionised calcium directly if available and the result will change management.