Comparison of two laboratory assays for PTH determination in hemodialysis patients

Introduction. The comparison between the new Tosoh ST AIA-Pack Intact PTH assay and the Elecsys Intact PTH Roche assay was carried out to assess how different the new laboratory assay for Intact 1-84 PTH determination is in comparison with a common assay such as the Elecsys, which is very similar to the Allegro assay used for the NKF-DOQI statements. Material and Methods.19 chronic stable hemodialysis patients were enrolled to check the PTH levels with the 2 assays. Median age was 71 (range 26-84 years), 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. Results. The median PTH value was 268 (range 35-1630 pg/dl) with the AIA-Pack vs. 184 (range 39-1225 pg/dl) with Elecsys (p=ns). AIA-Pack showed a Δ value of +38% in comparison to Elecsys and a median Bias of 27.4%. For PTH values < 150 pg/dl, 9 patients were detected with AIA-Pack (47.4%) vs. 9 patients detected with Elecsys (47.4%). For PTH values between 150 and 300 pg/dl, 6 patients were detected with AIA-Pack (31.6%) vs. 4 patients with Elecsys (21.0%). For PTH values >300 pg/dl 4 patients were detected with AIA-Pack (21.0%) vs. 6 patients with Elecsys (31.6%). A linear regression between the values of the two assays showed a good correlation (R = 0.9). Conclusions. The two PTH assays that were tested are very similar, however the attending physician should be aware of the differences when the patient changes his/her dialysis facility.