Clinical evaluation of new assays for determination of serum calcitonin concentrations

In order to test the clinical usefulness of new commercially available kits for determination of calcitonin serum concentrations, we investigated the family (N = 10) of a patient with medullary thyroid carcinoma and bilateral pheochromocytoma including his affected son, 10 athyreotic patients, totally thyroidectomized for non-medullary thyroid cancer, and 4 normal volunteers. Pentagastrin tests were performed in all subjects. Serum calcitonin levels before and after pentagastrin were determined by 4 kits. Kits A and B are immunoradiometric assays of the sandwich-type, kits C and D are radioimmunoassays, D being the one hitherto routinely used. Our results show that the new assays (kits A, B and C) have a better diagnostic accuracy in screening for medullary thyroid cancer than the RIA (kit D), hitherto used, where basal values overlapped with normals. Although basal values of normals were mostly near the detection limit of all 4 kits, kits A and B were sensitive enough to detect stimulation of calcitonin secretion by pentagastrin in all subjects with intact thyroid glands and kit C in most of them. The lack of increase in calcitonin after pentagastrin observed by kits A, B and C in athyreotic patients suggests deficiency of secretion of this hormone. Only kit D was unable to show this deficiency.