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.