THE PROCESS of diagnosing primary hyperparathyroidism has been one of exclusion of the other causes of hypercalcemia. In the past decade, since the measurement of parathyroid hormone (PTH) by radioimmunoassay became available through commercial laboratories, its use has grown rapidly. Theoretically, PTH levels should be elevated in primary hyperparathyroidism and possibly in malignancies producing PTH ectopically (pseudohyperparathyroidism); in the other causes of hypercalcemia, the levels should be decreased.1,2 The number of PTH assays ordered at this hospital has reached 350 per year, whereas during the period of 1970 to 1978 the number of new cases of primary hyperparathyroidism was less than ten per year. This suggested that many physicians were ordering PTH measurements early, if not even first, in the evaluation of hypercalcemia, the expectation being that PTH determinations would separate primary hyperparathyroidism from the other causes of hypercalcemia. Before direct measurements of PTH became available, laboratory tests reflecting a
Wong ET, Freier EF. The Differential Diagnosis of Hypercalcemia: An Algorithm for More Effective Use of Laboratory Tests. JAMA. 1982;247(1):75–80. doi:10.1001/jama.1982.03320260053034
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