Bio-intact parathyroid hormone and intact parathyroid hormone in hemodialysis patients with secondary hyperparathyroidism receiving intravenous calcitriol therapy.

Intact parathyroid hormone (iPTH) assay has been the most widely used for the diagnosis of secondary hyperparathyroidism and evaluation of vitamin D therapy. However, 1-84 PTH assay might be a better diagnostic tool since iPTH detects not only 1-84 PTH but also large C-terminal fragments, which would antagonize PTH action. Therefore, we conducted a multicenter study to evaluate the clinical usefulness of a newly developed immunochemiluminometric assay for 1-84 PTH, Bio-Intact PTH (BiPTH). Thirty-five uremic patients with secondary hyperparathyroidism participated in the study. Intravenous calcitriol therapy was continued for 12 months. iPTH and bone-specific alkaline phosphatase (BAP) were monitored at each dialysis center to control the dose of calcitriol. Serum and plasma samples were collected from each center and both iPTH and BiPTH were measured using Allegro-Lite assay reagents from Nichols Institute Diagnostics (San Clemente, CA, USA). Intravenous calcitriol suppressed iPTH after 1 month as well as BiPTH. Bone-specific alkaline phosphatase decreased after 3 months. A high degree of correlation between Nichols iPTH and BiPTH (y = 0.3913 x + 19.517, r = 0.9561) was demonstrated with a BiPTH/iPTH ratio of approximately 0.44. Significant correlation between BAP and iPTH, or between BAP and BiPTH was not observed. Our limited data failed to demonstrate the superiority of BiPTH to iPTH. Therefore, further investigations would be necessary to examine the relationship between BiPTH and bone histomorphometry.