Primary hyperparathyroidism: role of the preoperative oral calcium loading test in the differential diagnosis between adenoma and hyperplasia.

Whereas the sensitivity of the membrane calcium receptors is decreased in parathyroid adenoma, extracellular calcium may reduce parathyroid hormone (PTH) secretion through the protein kinase C pathway in parathyroid hyperplasia. The aim of this study was to determine the role of a preoperative oral calcium loading test in the differential diagnosis between adenoma and hyperplasia. Twenty-two subjects with adenoma (group A, age +/- standard error 56 +/-2 years, female/male 15/7), 10 individuals with hyperplasia (group H, age 54 +/-3, female/male 8/2), and 32 age and gender pair-matched controls (group C) underwent the test. Calcium and PTH were measured before and 60, 120, and 180 min after oral administration of 1 g of calcium (as gluconolactate). Product P was defined as minimal PTH concentration (pg/mL) x maximal calcium concentration (mg/dL) during the test. Ratio R was defined as relative PTH decline/relative calcium increase. The PTH decline during the test in group H was comparable to that of the controls. PTH decline <30%, Product P > 1,100, and Ratio R < 4 diagnosed adenoma with specificity of 100%, 90%, and 100%, respectively. PTH decline >60% diagnosed hyperplasia with specificity of 100%. The total accuracy of the test (65%) was comparable to that of technetium-99 m sestamibi scintigraphy (66%) and better than that of ultrasonography (58%). The test may discriminate patients with sporadic diffuse hyperplasia from individuals with solitary adenoma in cases of primary hyperparathyroidism with an indication for surgery.