Interpretation of serum calcium in patients with abnormal serum proteins.

Two hundred consecutive specimens received in this laboratory for "liver function tests" showed a wide range of abnormal protein concentrations. Calcium concentration correlated closely with albumin (r = 0.867) but less closely with total protein (r = 0.682). A simple formula for adjusting calcium concentration was derived from the regression equation of calcium on albumin. Adjusted calcium = calcium - albumin + 4.0, where calcium is in mg/100 ml and albumin in g/100 ml.Low calcium concentrations were found in 49 (24.5%) and raised concentrations in six (3%) of the 200 blood specimens taken for liver function tests. After adjustment, the 95% limits of the observed range were identical with the 95% limits of the normal range determined in this laboratory. Unlike adjustments based on total protein or specific gravity, the adjustment on albumin in 39 specimens which showed hypergammaglobulinaemia on electrophoresis gave normal calcium concentrations.