Comparison of three different immunoassay methods for the evaluation of intact parathyroid hormone levels in hemodialysis patients

Background. Intact parathyroid hormone (iPTH) assays react with the non-(1-84) molecular form of PTH. This form behaves as a carboxy-terminal fragment and accumulates during renal failure. We wanted to examine the variation of iPTH levels between the more commonly used different immunoassay methods in hemodialysis patients. Methods. Our study was designed to compare three commercial second-generation immunoassays based on electrochemiluminescent immunoassay (ECLIA), enzyme immunoassay (EIA) and immunoradiometric assay (IRMA) for intact PTH. The serum samples from 88 patients were collected and the iPTH concentrations measured. Results. The median iPTH (IRMA) concentration (99 pg/mL) was lower than both median iPTH (ECLIA) concentration (290.5 pg/ml; p < 0.001) and iPTH (EIA) concentration (369 pg/mL; p < 0.001). The Bland-Altman graphs, which are plots of the percentage differences between the two methods against their mean, suggested that the IRMA methods are not in agreement with the other methods. Conclusion. It would be useful to reduce the variability among the methods with the use of a more standardized calibrator and of the same specific antibodies that only recognize the active PTH molecule.