Estimating testosterone concentrations in adolescent girls: Comparison of two direct immunoassays to liquid chromatography-tandem mass spectrometry.

CONTEXT:The appropriate role of direct total testosterone (T) immunoassays in reproductive research is controversial. OBJECTIVE:To assess the concordance between two direct immunoassays and a liquid chromatography-tandem mass spectrometry (LC-MS/MS) assay for total T in adolescent girls with measured concentrations < 50 ng/dl. DESIGN:Cross-sectional analysis. SETTING:Academic medical center. PARTICIPANTS:Adolescent girls (age 8.4-18.1 years) participating in clinical research protocols. INTERVENTION:Paired blood samples were obtained for total T by LC-MS/MS (n = 66; Mayo Clinic Laboratory) and by direct immunoassay (Center for Research in Reproduction)-either radioimmunoassay (RIA; n = 31) or chemiluminescence immunoassay (CLIA; n = 35). At the time of assay, laboratories were unaware that results would be compared. MAIN OUTCOME MEASURE:Measurement agreement between immunoassay and LC-MS/MS. RESULTS:Measured T concentrations (LC-MS/MS) were <7 to 44 ng/dl. The average difference between RIA and LC-MS/MS was 0.84 [-0.89, 2.56] ng/dl (mean [95% confidence interval]). RIA correlated very strongly with LC-MS/MS (r = 0.899; p < 0.0001); and both Deming regression and Bland-Altman analysis suggested no bias. The average difference between chemiluminescence and LC-MS/MS was 1.39 [-0.83, 3.60] ng/dl. CLIA correlated strongly with LC-MS/MS (r = 0.806; p < 0.0001). While Bland-Altman analysis suggested no systematic bias, Deming regression analysis suggested that, as measured values increased, values obtained by CLIA tended to be progressively, albeit only modestly, higher than those obtained by LC-MS/MS. CONCLUSIONS:These data support the use of rigorously-performed and carefully-validated direct T immunoassays in high-quality endocrine research in peripubertal adolescent girls.