PTH in Dialysis

Mineral bone disease (MBD) affects nearly all patients with kidney failure requiring dialysis and requires surveillance of serum phosphate, serum calcium and parathyroid hormone (PTH) levels at regular intervals. Considerable controversy exists over the question which diagnostic assay should be used to measure and monitor PTH. The existence of PTH fragments, which became known to be detected by first and second generation PTH assays (second generation, also entitled “intact” PTH assays) led to the development of full-length PTH assays (third generation, also entitled “biointact” PTH assays) that detect only full length PTH (1-84).

Research question and objectives
Several studies have evaluated the correlation between various PTH assays at a single time-point, but no previous study had tested the hypothesis that longitudinal changes in PTH levels, which are important for making treatment decisions, can be monitored by several PTH assays alike. To this aim, our primary objective was to analyze the longitudinal variance in PTH over the course of 1 year, using each of two assays of the second and third generations, respectively. Secondary objectives included determining changes in serum phosphate, serum calcium, fibroblast growth factor 23 (FGF23), with respect to treatment decisions.

Patients and methods
Our hemodialysis center performs routine blood draws every quarter, the obtained laboratory values include routine chemistry, blood cell count, PTH and vitamin D. Among all hemodialysis patients who had generally agreed and signed consent to the research use of their superfluous sample specimen, we recorded demographics and hemodialysis treatment characteristics at baseline and over the course of 1 year. At every quarterly blood draw over the course of one year, we will froze away the serum from these patients and at the end of 4 quarters, we analyzed PTH-levels using the following assays: Intact Parathyroid Hormone (Advia Centaur, Siemens Healthcare), PTH-Intact (Cobas, Roche), PTH (1-84) - Biointact (Cobas, Roche), Liaison 1-84 PTH Assay (DiaSorin), respectively.