Comparison of Two Parathyroid Hormone Assays in Hemodialysis Patients

Parathyroid hormone (PTH) determination is essential for the diagnosis of renal osteodystrophy, but differences between the laboratory assays can lead to different therapies. This study compared the new Tosoh ST AIA-Pack Intact PTH assay (Tosoh Bioscience, San Francisco, CA, USA) with the Elecsys Intact PTH Roche assay (Roche Diagnostics GmbH, Mannheim, Germany), currently considered the gold standard. Nineteen chronic stable hemodialysis patients were enrolled to check PTH levels with the two assays. Median age was 71 years (range 26-84), M/F = 10/9. Blood samples were taken before the start of the same midweek dialysis session. Two blood vacuettes were collected and immediately transported to the central laboratory. The median PTH value was 268 (range 35-901 pg/dL) with the AIA-Pack versus 184 (range 39-552 pg/dL) with Elecsys. The Wilcoxon test showed a significant difference between the two methods (P < 0.0001). AIA-Pack showed a delta value of +38% in comparison with Elecsys and a median bias of 27.4%. For PTH values <150 pg/dL, nine patients were detected with AIA-Pack (47.4%) versus nine patients detected with Elecsys (47.4%). For PTH values between 150 and 300 pg/dL, six patients were detected with AIA-Pack (31.6%) versus four patients with Elecsys (21.0%). For PTH values >300 pg/dL four patients were detected with AIA-Pack (21.0%) versus six patients with Elecsys (31.6%). The two assays showed no differences for each of the three PTH ranges considered. The two PTH assays tested are different and the attending physician should be aware of the differences when patients change their dialysis facility.