Endocrine Abstracts

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.