Hydrocortisone suppression test and discriminant analysis in differential diagnosis of hypercalcaemia.

Experience is reported of the hydrocortisone suppression test in 140 hypercalcaemic patients, comprising 98 new cases of hyperparathyroidism and 42 cases of non-parathyroid malignant disease. The diagnostic accuracy of the test was compared in 168 patients with that of discriminant analysis, the discriminant functions being derived from plasma inorganic phosphate, alkaline phosphatase, chloride, bicarbonate, and urea, and the erythrocyte sedimentation rate. The hydrocortisone test and discriminant analysis each achieved a diagnostic accuracy of about 93% in 148 patients with either non-parathyroid malignant disease or hyperparathyroidism without osteitis fibrosa. When both tests pointed to the same diagnosis, they were wrong in less than 1% of cases. The hydrocortisone test was not helpful in patients with osteitis fibrosa. Both tests can be performed in any hospital with reliable standard laboratory services. Used in combination they have a high predictive value in distinguishing hypercalcaemia of parathyroid origin from that due to non-parathyroid malignant disease and have not led to errors of clinical importance. They should continue to play a major role in the differential diagnosis of hypercalcaemia until a prompt and reliable service finally establishes parathyroid hormone assay as the definitive laboratory procedure.