Total body retention of orally administered 47-calcium in primary hyperparathyroidism

Using a whole body radiation detector, we have measured the total body retention of 47-Ca 7 days after oral administration of the isotope to patients with various disorders of calcium metabolism. The percent retention of 47-Ca given with 90 mg of unlabeled (carrier) calcium varied with the calcium metabolic status as follows: normals (n equals 14), 33-43 percent (mean 38); primary hyperparathyroidism (n equals 28), 32-74 percent (mean 52); idiopathic hypercalciuria (n equals 9), 34-49 percent (mean 42); and hypercalcemia of other etiology (n equals 3), 23-26 percent (mean 25). Almost half (13/28) of those with hyperparathyroidism showed a retention above 55 percent, distinguishing them from subjects with idiopathic hypercalciuria. Retention of 47-Ca correlated poorly with clinical measures of severity of hyperparathyroidism. When isotope was diluted with a smaller amount of carrier calcium (20 mg), retention was increaseed in normals (n equals 5) to 46-54 percent (mean 50) and in hyperparathyroidism (n equals 5) to 64-87 percent (mean 73). After surgical cure of hyperparathyroidism retention of isotope returned toward normal in 5 of 7 subjects. Whole body retention of orally administered 47-Ca may prove useful in detecting hyperparathyroidism in subjects with mild hypercalcemia or hypercalciuria.