Carbon isotope ratio (δ13C) values of urinary steroids for doping control in sport

The detection of steroids originating from synthetic precursors in relation to their chemically identical natural analogues has proven to be a significant challenge for doping control laboratories accredited by the World Anti-Doping Agency (WADA). Endogenous steroid abuse may be confirmed by utilising the atomic specificity of gas chromatography-combustion-isotope ratio mass spectrometry (GC-C-IRMS) that enables the precise measurement of differences in stable isotope ratios that arise as a result of fractionation patterns inherent in the source of steroids. A comprehensive carbon isotope ratio (δ13C) profiling study (n = 1262) of urinary ketosteroids is reported that demonstrates the inter-individual variation that can be expected from factors such as diet, ethnicity, gender and age within and between different populations (13 countries). This δ13C distribution is shown by principal component analysis (PCA) to provide a statistical comparison to δ13C values observed following administration of testosterone enanthate. A limited collection of steroid diol data (n = 100; consisting of three countries) is also presented with comparison to δ13C values of excreted testosterone to validate criteria for WADA accredited laboratories to prove doping offences.