[A screening index for primary hyperparathyroidism using discriminant functions].

In order to obtain a useful screening index for primary hyperparathyroidism (PHPT), seven patients with PHPT and fifty-one patients with nonparathyroid hypercalcemia (NPHC) were studied retrospectively. Serum calcium, inorganic phosphate (IP), alkaline phosphatase, albumin (Alb), chloride (Cl), total protein, urea nitrogen and creatinine (Cre) were analyzed at the same time. Discriminant analysis using a stepwise variable select method was applied to these patients. A discriminant function (F 1) was derived from three laboratory tests; F 1 = -0.660 x [IP] + 0.142 x [Cl] + 0.564 x [Alb] - 14.4 (PHPT: F 1 greater than 0.641). F 1 had sensitivity of 100% and specificity of 72.5% (14 false positives) in diagnosing PHPT. Next, another discriminant function (F 2) was derived from PHPT and the false positive patients; F 2 = -2.61 x [IP] + 0.286 x [Cl] - 4.24 x [Cre] - 19.3 (PHPT: F 2 greater than 0.412). When F 2 was applied to positive patients by F 1, final sensitivity was 100% and specificity was 98%. This screening method was tested prospectively in fifty-six consecutive samples of hypercalcemia (PHPT 4, NPHC 52), resulting in sensitivity of 100% and specificity of 98%. It was proved that our screening method using two step discriminant functions was very useful to diagnose PHPT.