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

Context: 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.
Objective: 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.
Setting and Design: This prospective pilot study was conducted at the chronic hemodialysis unit of the Medical University of Vienna between December 2012 and September 2013.
Patients: We studied six male patients with CHD with elevated basal calcitonin levels.
Intervention: 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.
Main Outcome Measures: 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.
Results: 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.
Conclusions: In patients with CHD, the response of calcitonin to calcium and pentagastrin was comparable, making calcium a potential substitute for pentagastrin in these patients.