Comparison of intact PTH assay and whole PTH assay in long-term dialysis patients

Adynamic bone disease has become a major problem in long-term dialysis pati ents. It has been suggested that higher levels of parathyroid hormone (PTH) are needed to maintain normal bone turnover In uremia. PTH levels currentl y are evaluated routinely by Intact PTH assay, which may detect Inactive 7- 84 PTH fragments as well as 1-84 PTH. We examined the efficacy of whole PTH assay, which detects 1-84 PTH exclusively, in 99 nondiabetic patients on m aintenance dialysis for more than 10 years, without any residual renal func tion. PTH levels determined by whole PTH assay were lower than those determ ined by Intact PTH assay In all cases. Serum markers of bone metabolism, su ch as serum activity of bone alkaline phosphatase, correlated well with who le PTH levels. Because 7-84 PTH has been shown to Inhibit the effects of 1- 84 PTH, the biologic activity of circulating PTH in uremic patients may be much lower than the values assayed by conventional Intact PTH assay. Despit e an attempt to correlate 1-84 PTH/7-84 PTH ratio with bone histology, we c ould find only 1 patient out of 99 with 1-84 PTH/7-84 PTH ratio less than 1 , which has been suggested to be Indicative of low turnover bone. A cutoff value of this ratio should be set In the future for patients with a long he modialysis history, with various modes of medical therapy. (C) 2001 by the National Kidney Foundation, Inc.