High serum levels of a non-(1-84) parathyroid hormone (PTH) fragment in pediatric haemodialysis patients.

The measurement of serum intact parathyroid hormone (PTH) is routinely made in haemodialysed (HD) patients to diagnose and monitor secondary hyperparathyroidism. We measured pre- and post-dialysis serum ionized calcium (Ca2+) and PTH in 12 HD children (7 boys) aged 13.8+/-3.6 years. A group of 27 normal short-statured children served as controls. Serum PTH was assessed by a new assay (CAP) recognizing only the (1-84) molecule and an older one (Allegro) recognizing both the 1-84 and a non-(1-84) PTH equally. The concentrations obtained with the CAP assay were lower than those obtained with the Allegro assay both in controls and in HD patients. They were still lower in HD patients when expressed as multiples of the median of the control group. The Allegro/CAP ratio, was highly variable from one subject to another and was lower (P<0.0001) in controls (1.46+/-0.26) than in HD patients, both before (3.06+/-1.60) and after dialysis (2.94+/-0.65). During dialysis, Ca2+ increased significantly (P<0.0001) and PTH decreased significantly (P<0.0001) with both the CAP and the Allegro assays, but was more often normal or low with the CAP than with the Allegro assay. Although the two assays correlate well, they may provide different clinical information in some HD children which could lead to different therapeutic decisions.