Parathyroid hormone (PTH) monitoring that can differentiate between oxidized and nonoxidized forms of the substance is expected to improve the treatment of patients with end-stage renal disease (ESRD).
Patients with ESRD and PTH levels that are too low or too high are at increased risk for death. However, “current tests for parathyroid hormone levels overlook a key factor,” noted Berthold Hocher, MD, PhD, of the University of Potsdam in Potsdam-Rehbrücke, Germany, in a statement from The Endocrine Society. “When parathyroid hormone interacts with oxygen under conditions of stress such as end-stage renal disease, it becomes biologically inactive.”
Dr. Hocher and colleagues devised a new approach to PTH testing that he calls the first to distinguish between the nonoxidized, biologically active version of the hormone and the oxidized version. As the researchers described in the Journal of Clinical Endocrinology & Metabolism, they analyzed the association of nonoxidized PTH on mortality in hemodialysis (HD) patients using a new assay system. Of the 224 men and 116 women (median age 66 years) involved in this prospective cohort study, 170 (50%) died during the five-year follow-up period, usually as a result of cardiovascular disease, infections, or cancer.
According to blood samples taken throughout the study period, median levels of nonoxidized PTH were 7.2 ng/L among the survivors and 5.0 ng/L among the patients who had died during follow-up. Survival was increased among patients in the highest tertile of nonoxidized PTH levels, at a median 1,702 days compared with a median 453 days in the lowest tertile. Further analysis showed that higher age increased the odds for death, whereas higher levels of nonoxidized parathyroid hormone reduced the odds for death.
In another model analyzing a subgroup of HD patients with intact PTH (iPTH) concentrations at baseline above the upper-normal range of the iPTH assay (70 ng/L), mortality was associated with oxidized, but not with nonoxidized, parathyroid hormone levels.
The investigators concluded that the predictive power of nonoxidized parathyroid hormone and iPTH on the mortality of HD patients differs substantially, that measurements of nonoxidized hormone may reflect the hormone status more precisely, and that iPTH-associated mortality is most likely describing oxidative stress-related mortality.
“The nephrology community has long recognized there is an issue with current testing approaches,” Dr. Hocher said, “and now we can solve this problem and improve patient care.”