Context: There is no standardized assay of testosterone in women. Liquid chromatography mass spectrometry (LC/MS) has been proposed as the preferable assay by an Endocrine Society Position Statement.
Objective: The aim was to compare assay results from a direct RIA with two LC/MS.
Design and setting: We conducted a blinded laboratory study including masked duplicate samples at three laboratories--two academic (University of Virginia, RIA; and Mayo Clinic, LC/MS) and one commercial (Quest, LC/MS).
Participants and interventions: Baseline testosterone levels from 596 women with PCOS who participated in a large, multicenter, randomized controlled infertility trial performed at academic health centers in the United States were run by varying assays, and results were compared.
Main outcome measure: We measured assay precision and correlation and baseline Ferriman-Gallwey hirsutism scores.
Results: Median testosterone levels were highest with RIA. The correlations between the blinded samples that were run in duplicate were comparable. The correlation coefficient (CC) between LC/MS at Quest and Mayo was 0.83 [95% confidence interval (CI), 0.80-0.85], between RIA and LC/MS at Mayo was 0.79 (95% CI, 0.76-0.82), and between RIA and LC/MS at Quest was 0.67 (95% CI, 0.63-0.72). Interassay variation was highest at the lower levels of total testosterone (≤50 ng/dl). The CC for Quest LC/MS was significantly different from those derived from the other assays. We found similar correlations between total testosterone levels and hirsutism score with the RIA (CC=0.24), LC/MS at Mayo (CC=0.15), or Quest (CC=0.17).
Conclusions: A testosterone RIA is comparable to LC/MS assays. There is significant variability between LC/MS assays and poor precision with all assays at low testosterone levels.
Trial registration: ClinicalTrials.gov NCT00068861.