Adsorption of mycophenolic acid and its phenolic glucuronide to glass, polystyrene, and polypropylene containers.

2010 platform (Roche Diagnostics). Ionized calcium and 25-hydroxyvita-min D (Nichols Advantage) were also measured in all samples. Results for the healthy individuals are presented in Fig. 1. The bio-intact PTH values measured by the IRMA and chemiluminescence immunoas-say were, on average, 50% and 30% lower, respectively, than the PTH measured by the Elecsys. Regression analysis demonstrated significantly different slopes (P Ͻ0.001), but not intercepts, for both the IRMA and chemiluminescence immunoassay compared with the Elecsys assay. Most striking was the discordance between the ELISA and the IRMA, the chemiluminescence immunoas-say, and the Elecsys assay. Comparison between the ELISA and Elecsys revealed a significantly different intercept (P Ͻ0.001). The results obtained with the third-generation IRMA and the chemiluminescence immunoassay also differed, despite the good correlation, and regression analysis demonstrated a significant difference for the slope (P Ͻ0.001) but not for the intercept. The finding of higher results with the chemilumi-nescence immunoassay concurs with the results reported by Boudou et al. (3), but immunoreactivity does not seem to be implicated in these differences (1–3). In addition to the apparent differences in assay design, other possible reasons for the lack of agreement between the assays investigated could be matrix effects and/or differences in standardization. The problems hampering immunoassay standardization are many and vary for different analytes, as has been reviewed by Stenman (4). Thus, the use of independent reference intervals for each of the bio-intact PTH assays is clinically important. We observed no significant differences between healthy individuals and patients with predialysis chronic kidney disease for 25-hydroxyvita-min D, but mean concentrations of bio-intact PTH (by chemilumines-cence immunoassay; P Ͻ0.001) and ionized calcium (P Ͻ0.05) were higher in the patients. PTH measured by Elecsys was, on average, 75% higher than the measured bio-intact PTH in patients, consistent with the expected presence of high concentrations of circulating PTH fragments in patients with impaired renal function. In addition, the distribution of bio-intact PTH analyzed by the chemiluminescence immunoas-say (mean, 71 ng/L; range, 5–227 ng/L) was wider in the patient group than in the healthy individuals [23 (11–50) ng/L]. Despite our strict adherence to the ELISA protocol and 3 independent runs with the same set of samples, this assay generated inconsistent results , which require additional meth-odologic studies to fully explain. We conclude that although the third-generation bio-intact PTH ELISA requires further evaluation, the chemi-luminescence immunoassay and IRMA are comparable. Development of a novel immunoradiometric assay exclusively …