Results of the calcitonin stimulation test in normal volunteers compared with genetically unaffected members of MEM 2A and familial medullary thyroid carcinoma families

: In the multiple endocrine neoplasia (MEN) type 2A and in the familial medullary thyroid carcinoma (FMTC), the recent development of genetic testing has provided new methods of identifying disease gene carriers. The use of sensitive immunoradiometric calcitonin (CT) assays led us to evaluate reference ranges of plasma CT responses after pentagastrin in healthy subjects in order to discuss the place of pentagastrin testing in the management of hereditary MTC. Basal and pentagastrin-stimulated CT concentrations were measured in 71 healthy volunteers--aged 20-67 years--and 76 genetically unaffected members of families with hereditary MTC--aged 4-61 years. In healthy subjects, CT peak values were below 30 ng/l in 68 cases and below 50 ng/l in 3 cases. In the genetically unaffected patients, CT peak values were below 15 ng/l in young patients and below 30 ng/l in patients older than 19 year excepted 5 men with stimulated CT levels ranging from 36.5 to 52 ng/l. In 2 of these 5, thyroidectomy revealed C-cell hyperplasia. Borderline test results are not sufficient to establish diagnosis of MTC and in these familial syndromes, management has to be based on the results of genetic testing. However, the determination of the upper normal limit for stimulated CT concentrations in young patients (< 15 ng/l) may help to identify the optimal moment for surgery.