Development of a highly sensitive and specific new testosterone time-resolved fluoroimmunoassay in human serum

A new time-resolved fluoroimmunoassay (TR-FIA) of testosterone in serum is described, using a biotinylated testosterone tracer, with a long spacer arm between biotin and testosterone, coupled to the C3 of the testosterone: a biotinylaminodecane carboxymethyloxime testosterone. This tracer affords a great sensitivity of the standard curve, because a amount of 0.3 pg of testosterone can be significantly measured on the testosterone standard curve. The "functional" sensitivity is at least equal to 21 pg/ml of serum. The specificity of the assay is insured by a celite chromatographic step on new minicolumns before immunoassay. The variation coefficient of inter-series reproducibility measured on low and normal testosterone levels in untreated and testosterone treated hypogonadal men were between 2.17 and 5.07%. The accuracy test, (overload and dilution tests) gave satisfying results. Moreover, in a comparison with GCMS, it appeared that the correlation coefficient was 0.992 and no significant difference could be exhibited between the two methods. Consequently, this specific, sensitive reproducible and easy to use method is well suited to the measurement of testosterone in clinical and pharmacological conditions.