Endocrine Abstracts

Background: The ‘intact’ parathyroid hormone (PTH) assays recognizes PTH (1–84) as well as amino terminally truncated fragments (C-PTH fragments). The present study investigated whether the use of plasma PTH-(1–84)/C-PTH fragment ratio enhances the noninvasive assessment of bone metabolism in patients on dialysis.

Methods: Blood samples of 45 healthy subjects with normal ‘intact’-PTH values and 135 samples of dialysis patients were collected from laboratory routine. The samples of the dialysis patients were classified in order of their ‘intact’-PTH levels: 45 with a ‘intact’-PTH value <100 pg/ ml, 45 with a ‘intact’-PTH value between 100 and 500 pg/ ml, and a third group with ‘intact’-PTH levels above 500 pg/ ml. The determination of the ‘intact’-PTH was performed on a ROCHE E170 analyzer with the Elecsys PTH assay. The testing of PTH-(1–84) and of OSTASE (BAP) as a parameter of osteoblast activity was perfomed on a DiaSorin LIAISON analyzer with the LIAISON PTH3 assay and the LIAISON BAP Ostase assay respectively. Blood levels of large C-PTH fragments were calculated by subtracting PTH-(1–84) from ‘intact’-PTH.

Results: Both plasma intact- and PTH-(1–84) were significantly higher in patients with high and normal Ostase levels as a parameter of bone turnover, whereas the calculated C-PTH fragments were similar. Patients with low Ostase levels had significantly more C-PTH fragments than PTH-(1–84) (P<0.001), whereas patients with high or normal bone turnover had significantly more PTH-(1–84) than C-PTH fragments (P< 0.001), and the PTH-(1–84)/C-PTH fragment ratio was significantly higher than in patients with high or normal (range of 0.66–12.2) than low bone turnover (range of 0.1–0.88).

Bone turnover is reflected by the balance between the relative amount of circulating PTH-(1–84) and the large C-PTH fragments. The data lend support to the notion of an antagonistic effect of the C-PTH fragments on the PTH-(1–84) action on bone. The wide range of the obtained resuts in the PTH-(1–84) / C-PTH fragments ratio demonstrates that a simple fixed percentage of intact PTH cannot be identified for prediction of the large C-PTH fragments.

Conclusions: The PTH-(1–84) / C-PTH fragment ratio predicts bone turnover with acceptable precision for biological measurements.

Declaration of interest: The authors declare that there is no conflict of interest that could be perceived as prejudicing the impartiality of the research project.

Funding: This research did not receive any specific grant from any funding agency in the public, commercial or not-for-profit sector.