A Putative Testosterone Precursor Helps to Overcome ABP Limitations in Doping Detection for Low Urinary Testosterone...

In doping control, the primary strategy for confirming testosterone (T) and its metabolites relies on triggering Isotope Ratio Mass Spectrometry (IRMS) via abnormalities in the Athlete Biological Passport (ABP). However, this approach is often ineffective in populations with low baseline T, such as females or individuals with UGT2B17 deletions, where ABP fluctuations are too subtle to trigger an IRMS investigation. To address this limitation, this study introduces a novel strategy that utilizes a putative T precursor as a specific trigger for IRMS analysis. Three volunteers (Male 1, with normal urinary T; Male 2, with low urinary T; and a female) were administered a single 40-mg oral dose of 6β-Cl-T. Urinary steroid profiles were monitored by GC-MS/MS, and the exogenous origin of steroids was confirmed by GC-C-IRMS. Male 1 exhibited an atypical ABP that triggered IRMS confirmation, revealing exogenous T administration. In contrast, Male 2 and the female volunteer showed negligible ABP variations, insufficient to trigger analysis and posing a high risk of false-negative results. However, the novel metabolites (G1 and M1) were detected in the urine samples of all three volunteers. Using the new metabolites as a new trigger criterion, we subsequently conducted IRMS analysis on Male 2 and the female, which confirmed the presence of exogenous T and its metabolites. These findings suggest G1 or M1 is a putative biomarker for detecting exogenous AAS in low-level T populations, particularly UGT2B17 deletion males and females.