Laboratory Tests in the Diagnosis of Hyperparathyroidism in Hypercalcemic Patients

The results of tests of serum phosphate concentration or urine calcium or phosphate excretion, either under controlled conditions or after infusion of calcium or phosphate, were examined for their value in diagnosing primary hyperparathyroidism. The results of these tests were compared in hypercalcemic patients with primary hyperparathyroidism, normal subjects, patients with renal stones, and patients with hypercalcemia caused by nonparathyroid tumors. Published data and our own experience demonstrate that these tests are all insensitive and nonspecific for the diagnosis of primary hyperparathyroidism. Patients with hypercalcemia should be examined for all possible causes of hypercalcemia, and when none can be identified a diagnosis of primary hyperparathyroidism should be considered. Unfortunately, none of the tests we have discussed will confirm the diagnosis of primary hyperparathyroidism. The most difficult cases to identify are those of hypercalcemia caused by primary hyperparathyroidism and nonparathyroid malignant neoplasms without demonstrable bony metastases. In the latter patients the clinical and laboratory findings may be indistinguishable from those of patients with primary hyperparathyroidism. In hypercalcemic patients in whom primary hyperparathyroidism is suspected the decisions of whether to perform a parathyroid exploration should be based primarily on the signs, symptoms, and prognosis of the particular patient rather than on the results of any of the tests analyzed in this report.