Value of measuring C-terminal parathyrin in differential diagnosis of hypercalcemia

We measured calcium, phosphate, chloride, albumin, C-terminal parathyrin, and beta 2-microglobulin in serum from 102 hypercalcemic patients: 42 with primary hyperparathyroidism and 60 with neoplasia. The calcium concentrations and the discriminant function index of Johnson et al. (Clin Chem 28, 333-338, 1982) were higher in malignant hypercalcemia than in primary hyperparathyroidism. The diagnostic efficiency of the index and of parathyrin concentration was 82% and 78%, respectively. Using the ratio of parathyrin to beta 2-microglobulin increased the diagnostic efficiency to 98%; the ratio of the discriminant index to parathyrin concentration had a diagnostic efficiency of 100%. We conclude that C-terminal assay by itself is no better than the discriminant function index.