Variability of Parathyroid Hormone and Other Markers of Bone Mineral Metabolism in Patients Receiving Hemodialysis

Abstract

Clinical management of mineral bone disorder in patients with kidney failure is guided by biochemical targets, in particular parathyroid hormone (PTH) concentration. The biologic variation of PTH and other bone mineral markers was measured in hemodialysis patients to better define their role in management. Intact PTH, biointact (whole-molecule) PTH, calcium, albumin-adjusted calcium, phosphate, and alkaline phosphatase (ALP) were measured in nonfasting samples obtained twice a week (both short-dialysis interval) over a 6-week period in 22 stable hemodialysis patients. Concurrently, samples were obtained from 12 healthy volunteers. Intraindividual coefficients of variance (CVI) were calculated and used to derive the reference change value (RCV) required to be 95% certain that a change has occurred. CVI of all markers was significantly (P<0.05) greater in patients than in healthy volunteers. For phosphate, ALP, and PTH this implies that an increased number of samples is required to estimate an individual's homeostatic set point. CVI of intact PTH was 25.6% in hemodialysis patients and 19.2% in healthy volunteers. A greater RCV should be used for patients (72%) compared with healthy volunteers (54%). Ideally 26 specimens should be measured to estimate a patient's intact PTH homeostatic set point (within +/-10%) with 95% probability. The CVI of biointact PTH was at least as high as that for intact PTH. The uncertainty of PTH estimation in an individual significantly undermines its value as a tool in the management of chronic kidney disease-mineral bone disorder using current management approaches.