Laboratory differentiation of hypercalcemic patients.

We studied the biochemical discrimination of primary hyperparathyroidism from other causes of hypercalcemia. This potentially serious disorder is readily remedied, and because recent work has suggested that even very mild cases in elderly people derive substantial benefit from surgery, the correct diagnosis is crucial. A discriminant function is derived that maximizes the use of data that are readily available from general hospital laboratory; application of the Hamilton "T score" system simplifies its interpretation. We conclude that the best use of this formula is as a negative discriminant, to identify some non-hyperparathyroid cause of hypercalcemia, and also as a partial positive discriminant, to identify some cases of primary hyperparathyroidism. We review previous such discriminants and consider the reasons why they have been less successful.