First- and second-generation immunometric PTH assays during treatment of hyperparathyroidism with cinacalcet HCl

Kidney Int. 2005 Sep;68(3):1236-43. doi: 10.1111/j.1523-1755.2005.00517.x.


Background: First-generation immunometric assays for "intact" parathyroid hormone (iPTH) also measure large N-terminally truncated PTH fragments, whereas second-generation assays, such as the "bio-intact" PTH (biPTH) assay, measure only full-length biologically active PTH(1-84). This study compared iPTH and biPTH assays during cinacalcet treatment in subjects with secondary HPT receiving dialysis.

Methods: Four hundred and ten subjects were enrolled in a 26-week randomized, double-blind, placebo-controlled trial of oral cinacalcet (or placebo), 30 to 180 mg once daily, and efficacy was assessed using biPTH and iPTH assays.

Results: Compared with control treatment, cinacalcet improved the management of secondary HPT. Both biPTH and iPTH decreased by 38%+/- 3% during weeks 13 to 26 in the cinacalcet group; biPTH increased by 23%+/- 4% and iPTH increased by 9.5%+/- 3% in the control group (P < 0.001). Fifty-six percent of cinacalcet subjects and 10% of control subjects had a > or = 30% reduction in biPTH, and 61% and 11%, respectively, had a > or = 30% reduction in iPTH. Significant correlations between biPTH and iPTH levels were observed throughout the study. Both assays correlated similarly with bone-specific alkaline phosphatase levels. The ratio of biPTH to iPTH was maintained at 56% +/- 1% after treatment in both treatment groups. Increasing serum calcium levels were associated with a decreasing ratio of biPTH to (iPTH-biPTH).

Conclusion: These data show that PTH can be monitored with either iPTH or biPTH assays during therapy with cinacalcet, and that cinacalcet therapy does not exert a major influence on the ratio between PTH(1-84) and large, N-terminally truncated PTH fragments.

Publication types

  • Multicenter Study
  • Randomized Controlled Trial

MeSH terms

  • Adult
  • Aged
  • Calcium / blood
  • Cinacalcet
  • Drug Monitoring / methods
  • Female
  • Humans
  • Hyperparathyroidism / blood*
  • Hyperparathyroidism / drug therapy*
  • Immunoassay / methods*
  • Linear Models
  • Male
  • Middle Aged
  • Naphthalenes / administration & dosage*
  • Parathyroid Hormone / analysis
  • Parathyroid Hormone / blood*
  • Phosphorus / blood
  • Treatment Outcome
  • Vitamin D / blood


  • Naphthalenes
  • Parathyroid Hormone
  • Vitamin D
  • Phosphorus
  • Calcium
  • Cinacalcet