Calcium-Mediated Parathyroid Hormone Suppression to Assess Progression of Secondary Hyperparathyroidism During Treatment Among Incident Dialysis Patients

Context: Parathyroid gland function is affected adversely by tissue hyperplasia and gland enlargement in hyperparathyroidism. Objective: We examined the effects of 2 treatment strategies on the progression of secondary hyperparathyroidism using measurements of the nonsuppressible component of calcium-regulated PTH secretion as an index of parathyroid mass. Design, Subjects, and Intervention: In this randomized, open-label study, subjects managed with hemodialysis for >3 but <12 months before entering the trial (mean, 7.2 months) who had baseline plasma PTH levels >300 pg/mL received cinacalcet and low-dose vitamin D sterols (Cin-D, n = 153) or larger, varying doses of calcitriol, or other vitamin D analogs (Flex-D, n = 151). Study drug doses were adjusted periodically based on PTH and serum total calcium determinations. Main Outcome Measures: The exploratory endpoint was calcium-regulated PTH release, assessed using a standardized PTH suppression test before and after 52 weeks of treatment and 4 weeks after withdrawing treatment. PTH and serum total calcium were measured before hemodialysis using high-calcium (3.5 mEq/L or 1.75 mmol/L) dialysate and after 150 and 180 minutes. Results: Mean (95% confidence interval) nonsuppressible calcium-regulated PTH release at baseline did not differ between Cin-D, 33.4% (25.9%, 40.9%), and Flex-D, 28.1% (23.2%, 32.9%). Corresponding values after 52 weeks of treatment were 34.3% (29.7%, 38.9%) and 42.0% (32.7%, 51.3%), not significant, and did not change measurably in either group when reevaluated 4 weeks after treatments were withdrawn. Conclusion: Disease progression over 12 months was not documented using a PTH suppression test in this population. Calcium-mediated PTH suppression was maintained fully, however, in Cin-D despite reductions in serum total calcium concentration, whereas values did not increase in Flex-D despite substantial increases in serum calcium. (J Clin Endocrinol Metab 98: 618-625, 2013)