ISSN 1470-3947 (print) | ISSN 1479-6848 (online)

Endocrine Abstracts (2008) 16 P631

Development of an ElecsysR Testosterone II Immunoassay with an improved performance for measurement of testosterone in women

Judit Oldekamp, Klaus Hirzel, Erich Schneider & Dieter Gassner

Roche Diagnostics GmbH, Penzberg, Germany.

Immunoassays for testosterone produce sometimes incorrectly high results in female samples. The reasons of this phenomenon are not fully understood, but interference by cross-reacting substances and inaccurate calibration can be critical. One known endogenous interfering substance is dehydroepiandrosterone sulphate (DHEA-S). Other substances still have to be identified.

An Elecsys® Testosterone II assay using a new high affinity sheep monoclonal antibody (Bioventix SMA testo3.6A3) is currently in the development pipeline for the Elecsys and cobas e immunoassay platforms. The new assay shows improved recovery if compared with sensitive liquid chromatography tandem mass spectroscopy (LC-MS/MS). In method comparison studies with routine samples versus current Elecsys® Testosterone assay the number of some falsely elevated results is decreased. In addition, the cross-reactivity with DHEA-S and some other potentially interfering substances is reduced. The high affinity of the sheep monoclonal antibody for testosterone enables a low sample volume (20 μl) as well as an inclusion of a high protein content in the assay buffer. As a consequence an enhanced robustness against interferences caused by a variability in the sample matrix is obtained.

The new assay uses a delayed competitive test principle. Firstly, sample is incubated with the biotinylated antibody. Binding sites of the labelled antibody become occupied partly by the sample analyte. Secondly, streptavidin-coated microparticles and ruthenium-labelled hapten are added. Still free binding sites are occupied by the hapten conjugate. Total assay time is 2×9 min. The measuring range of the assay extends from ~0.02 to 15 ng/ml.

The Elecsys® Testosterone II shows improved correlation with LC-MS/MS and provides total imprecision and functional sensitivity that will meet customers needs.

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