Multicentre evaluation of an enzyme-immunoassay for cortisol determination.

The present paper describes a multicentre evaluation of a one step enzyme-immunoassay for the determination of cortisol in serum or plasma. Data from the investigation were analysed in terms of imprecision, detection limit, and correlation with other test methods. Within-run and between-run imprecisions (coefficient of variation) of Enzymun-Test Cortisol were less than 8% and 12%, respectively. The detection limit was 30 nmol/l (11 micrograms/l). With the exception of prednisolone, only low interference was found with other endogenous steroids. A good correlation between Enzymun-Test Cortisol and HPLC, LIA, FPIA and RIA was registered, although the latter two methods showed a scattering of regression lines from the different evaluators. The results show that Enzymun-Test Cortisol can be recommended as an alternative for the measurement of cortisol. As the method is calibrated against isotope dilution-mass spectrometry, results obtained with Enzymun-Test Cortisol are in agreement with the reference method.