Hebestreit, M., Flenkera, U., Fusholler, G., Geyer, J., Guntnera, U., Mareck, U., Piper, T., Thevis, M., Ayotte, C., & Schanzer, W. (2006). Determination of the origin of urinary norandrosterone traces by gas chromatography combustion isotope ratio mass spectrometry. Analyst, 131, 1021-1026.

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". . . 19-norandrosterone (NA) is the most abundant metabolite of the synthetic anabolic steroid 19-nortestosterone and related prohormones. On the other hand, small amounts are biosynthesized by pregnant women and further evidence exists for physiological origin of this compound. The World Anti-Doping Agency (WADA) formerly introduced threshold concentrations of 2 or 5 ng of NA per ml of urine to discriminate 19-nortestosterone abuse from biosynthetic origin. Recent findings showed however, that formation of NA resulting in concentrations in the range of the threshold levels might be due to demethylation of androsterone in urine, and the WADA 2006 Prohibited List has defined NA as endogenous steroid. To elucidate the endogenous or exogenous origin of NA, 13C/12C-analysis is the method of choice since synthetic 19-nortestosterone is derived from C3-plants by partial synthesis and shows 13CVPDB-values of around 28. Endogenous steroids are less depleted in 13C due to a dietary mixture of C3- and C4-plants. An extensive cleanup based on two high performance liquid chromatography cleanup steps was applied to quality control and doping control samples, which contained NA in concentrations down to 2 ng per ml of urine. 13C/12C-ratios of NA, androsterone and etiocholanolone [19-NE] were measured by gas chromatography/combustion/isotope ratio mass spectrometry. By comparing 13CVPDB-values of androsterone as endogenous reference compound with NA, the origin of NA in doping control samples was determined as either endogenous or exogenous."

Implication. This study describes a procedure for determining if 19-NA levels are solely exogenous or inflated by the within urine sample demethylation of andrsterone. Without 19-NA 19-NE, and androsterone values, it cannot be established that low levels of 19-NA in a sample are simply exogenous. When a positive test for 19-NA is recorded in a testing laboratory, the sample should be subjected to further analysis to determine the presence of other substances as well as comparing those covariate substances against standard controls. It is highly likely that a positive 19-NA drug test could be a false-positive.

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