Comparison of 1-84 and intact parathyroid hormone assay in pediatric dialysis patients.

The non-invasive diagnosis of renal osteodystrophy (ROD) in patients with end-stage renal disease (ESRD) remains dependent on the determination of an accurate parathyroid hormone (PTH) level. Older assays that determine the "intact" PTH molecule are known to cross react with various PTH fragments, resulting in overestimation of PTH levels. Recently, assays that determine the whole 1-84 PTH molecule have been made available. Monthly PTH values in chronic dialysis patients at our institution were compared using the Nichols Bio-Intact PTH (BiPTH, 1-84 PTH) and the intact PTH (iPTH) assay over 3 consecutive months. One hundred twenty-four samples were obtained from 51 (29 male) pediatric dialysis patients (27 HD). The mean patient age was 14.2+/-5.6 years (1.8-25.7 years), with 12 patients<10 years and 15 patients <30 kg. The mean 1-84 PTH/iPTH ratio was 0.48+/-0.11. While BiPTH values correlated closely with iPTH values ( r =0.98, P <0.05), we observed significant intra-patient (16.4+/-15.4%; range: -73.9 to 67.7%, total % error: 47.2%) and inter-patient (17.2+/-18.9%; range: -73.9 to 129.9%, total % error: 55%) variability in the 1-84 PTH/iPTH ratio over the 3-month study period. Thus, our findings suggest that ROD management based on prior associations between iPTH levels and bone biopsy findings should not be extrapolated using the newer 1-84 PTH assay.