Naoko Miwa a , Kosaku Nitta a , Naoki Kimata a , Yoshihiko Watanabe a , Koichi Suzuki a , Akira Kawashima b , Masahiro Haga c , Ryo-ichiro Watanabe c , Takanao Aoki c , Takashi Akiba b , Hiroshi Nihei a
17 November 2004
Background/Aim: It has been suggested that higher levels of parathyroid hormone (PTH) are required to maintain normal bone turnover in chronic hemodialysis (HD) patients. Serum PTH levels determined by intact PTH (i-PTH) assay may overestimate the actual activity of circulating PTH in HD patients. The aim of the present study was to assess the clinical usefulness of whole PTH assay on the evaluation of bone turnover in HD patients. Materials and Methods: We performed measurement of parameters on bone turnover in 179 HD patients (116 men, 63 women; mean age 61.0 ± 13.1 years). Serum whole PTH levels were determined as cyclase-activating PTH (CAP) by an immunoradiometric assay, and compared with those of i-PTH. Cyclase-inactivating PTH (CIP) was calculated as (i-PTH-CAP). The correlations between serum whole PTH levels and clinical parameters such as serum levels of Ca, P, bone alkaline phosphatase (BAP), bone Gla protein (BGP), total protein (TP), albumin (Alb), urea nitrogen (SUN), and creatinine (Cr) were analyzed using multivariate analysis. Results: The mean values of i-PTH and CAP were 124.1 ± 97.4 and 86.9 ± 71.6 pg/ml, respectively, indicating that the serum CAP levels were about 70% of i-PTH levels. The serum CAP levels significantly correlated with that of i-PTH (r = 0.959, p < 0.001). Moreover, a significant positive correlation between serum CAP levels and metabolic bone markers such as BAP (r = 0.400, p < 0.01) and BGP (r = 0.481, p < 0.01) was observed. Stepwise multivariate analysis revealed that serum levels of CAP were significantly determined by serum levels of Ca, P, Alb, and oral dosage of vitamin D (F ratio = 18.81, adjusted r<sup>2</sup> = 0.302). Conclusions: These data suggest that the biological activity of circulating PTH in HD patients is lower than the levels estimated by conventional i-PTH assay.