Measurement of total testosterone in women: comparison of a direct radioimmunoassay versus radioimmunoassay after organic solvent extraction and celite column partition chromatography

To evaluate the clinical usefulness for the measurement of testosterone (T) values in the “low” female range with a direct radioimmunoassay (RIA) for total T by comparing total T values measured by this assay with values determined by conventional RIA after organic solvent extraction/column chromatography. Cross-sectional study. Victoria, Australia. Two hundred fifty-nine healthy women, aged 18–75 years, recruited from the community. Fasting serum samples were obtained and stored at −80°C. Total T measurement. Total T was measured by the direct RIA method using antibody-coated tubes and iodine-labeled T tracer. For comparison, total T levels were also measured using the conventional RIA method after organic solvent (ethyl acetate:hexane [3:2]) extraction and celite column partition chromatography before RIA. The mean T level by direct RIA was 0.76 nmol/L (median, 0.70; SD, 0.54; minimum, 0.10; maximum, 3.2). The mean difference between the two measurements (direct RIA − conventional RIA) was −0.28 (SD, 0.3). The direct RIA value was 63% (95% confidence interval, 26%–155%) of the conventional RIA estimate. For the classification of values at the lower end of the range, there was very good agreement beyond chance (kappa = 0.68–0.74) for values in approximately the lowest 10th–40th percentiles. The direct RIA is a clinically useful assay for the study of the issue of “low” T within the female population.