Calcium fractions in serum of patients with thermal burns.

Total calcium measurement is less useful clinically than assay of the physiologically active fractions, free and ionized calcium. The latter were measured in burned patients by ultrafiltration and by ion-selective electrode. Hypocalcemia was observed in these patients but it was generally limited to low total calcium. On average, free or ionized calcium were in the normal range. Total and free calcium were weakly correlated with severity of burn injury suggesting a loss of several forms of calcium in severe burn injury. An algorithm was derived to allow calculation of free calcium from total calcium and albumin. Interpatient variables are important, however, so that the algorithm should not be substituted for actual assay of free and ionized calcium.