Interference of sex-hormone binding globulin in the "Coat-A-Count" testosterone no-extraction radioimmunoassay.

We evaluated a "no-extraction" assay system for serum testosterone [Diagnostic Products "Coat-A-Count" testosterone (direct)] with respect to the influence of sex-hormone binding globulin (SHBG). We conclude that the SHBG concentration strongly affects this estimation. The quantity of testosterone measured in the presence of 90 nmol of SHBG per liter (the upper reference limit of SHBG for women) was only about 40% of that measured at the lower limit of the SHBG reference interval (30 nmol/L). For SHBG concentrations less than 30 nmol/L one can expect the testosterone concentrations measured to be relatively too high.