Low-dose calcium versus pentagastrin for stimulation of calcitonin in chronic hemodialysis patients: a pilot study.

Elevated calcitonin levels occur in up to 46% of patients with chronic hemodialysis (CHD) and frequently reflect benign C-cell hyperplasia rather than medullary thyroid carcinoma. For the differential diagnosis of hypercalcitoninemia, the pentagastrin-stimulated calcitonin test was used until its availability became restricted. This study sought to compare calcium and pentagastrin in terms of their ability to stimulate calcitonin secretion and their side effects in patients with CHD. This prospective pilot study was conducted at the chronic hemodialysis unit of the Medical University of Vienna between December 2012 and September 2013. We studied six male patients with CHD with elevated basal calcitonin levels. The stimulation test was performed first with 0.5 μg/kg pentagastrin and then with 1 mg/kg calcium after a median washout period of 7 (6-9) months. We measured calcitonin, serum ionized calcium, intact PTH (iPTH), and C-terminal fibroblast growth factor 23 levels before and 2, 5, and 10 minutes after iv infusion of the stimulant and assessed the tolerability of the two substances by a questionnaire. Both pentagastrin and calcium significantly stimulated calcitonin secretion at 2 and 5 minutes. Partial correlation analysis revealed a strong association between calcium- and pentagastrin-stimulated calcitonin levels (r=0.875, P < .0001). Only after calcium infusion serum ionized calcium levels increased from 1.09 (0.91-1.16) mmol/l to 1.4 (1.14-1.65) mmol/l at 2 minutes (P < .01) but returned to baseline levels at 5 minutes. Moreover, calcium infusion led to a significant decrease in iPTH levels from 315 (203-723) pg/ml to 182 (121-415) pg/ml at 5 minutes (P < .05) and 171 (91-346) pg/ml at 10 minutes (P < .001). In general, calcium caused fewer and less severe side effects than pentagastrin. In patients with CHD, the response of calcitonin to calcium and pentagastrin was comparable, making calcium a potential substitute for pentagastrin in these patients.