Comparison of two competitive enzyme immunoassay kits for quantification of plasma Urotensin-II in rats

Changes in Urotensin-II (U-II) concentration, a potent vasoconstrictor peptide, have been detected in various pathologies, but it has been impossible to define a normality range. We aimed to analyze the concordance and interchangeability between two enzyme immunoassay methods developed by Phoenix Pharmaceuticals, Inc. to measure U-II plasma concentration in rats: ELISA and fluorescent EIA. Assays resulted positively correlated (r = 0.850; p < 0.01). There was a significant difference between assays values (p < 0.001). The analysis of agreement (Bland and Altman plot) stated that the mean of the differences was 2.055 (SD ± 0.588). Hence, we concluded that the two U-II assays were correlated but not interchangeable.