References Joop Ten Kate 3 Ionic Cross Talk Can Lead to Overestimation of 3-methoxytyramine during Quantification of Metanephrines by Mass Spectrometry

sample extraction further improved the accuracy of the 2 second generation assays in the low range (Table 1; also see online Supplemental Data Fig. 1), which indicates that they still suffer from interfering compounds and their specificity can be further improved. For several immunoassays an increased bias was observed (Table 1); this finding could be explained by the design of the assay, which is not calibrated for a purified reconstitution matrix. The phenomenon that direct automated testosterone immunoassays give inaccurate high results in samples from women and children because of possible calibration and specificity problems has been addressed extensively in the literature. The precise nature of the interfering compounds has yet to be elucidated, although a significant cross-reactivity with DHEA sulfate has been reported for the Cobas I and II assays (5 ). In the present study we evaluated the accuracy before and after sample extraction of 7 commercially available direct testosterone assays. In conclusion, in the 4.0 nmol/L testosterone range, all immunoassays showed a good correlation with ID-LC-MS/MS. The correlation coefficients for automated immunoassays were relatively poor for measurement of low testosterone concentrations ( 4.0 nmol/L) in untreated samples. Following diethyl ether sample extraction, the correlation coefficient of 6 of 7 immunoassays, including the second generation assays, increased. Although the accuracy of testosterone immunoassays has been improved since 2007 by the introduction of second generation assays, there is still a need for further improvement.