# Exogenous Versus Endogenous Nandrolone in Doping Investigations: A Systematic Literature Review
## 3 Results
\begin{table}
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**Authors** & **Analytical Techniques** & **Concentrations Found** \\ \hline [PERSON] (2018) [53] & GC-C-IRMS & Not clearly reported \\ \hline [PERSON] et al. (2018) [54] & GC-MS/MS & Not clearly reported \\ \hline [PERSON] et al. (2018) [55] & GC-MS/MS & Before consumption of the test meal, no 19-NA was detected in urine samples. The concentrations after one hour were 1 ng/mL. Highest 19-NA concentrations were reached after 4 h with 4 ng/mL and 8 ng/mL. \\ \hline [PERSON] (2018) [56] & GC-C-IRMS & Method validation \\ \hline [PERSON] et al. (2019) [57] & GC-C-IRMS & Method validation \\ \hline [PERSON] et al. (2020) [58] & LC-MS/MS & Not clearly reported \\ \hline [PERSON] et al. (2020) [59] & GC-MS/MS and GC-C-IRMS & 19-NA was not detected in the urine samples before the ingestion of the boar meat. After consumption, the two highest concentrations were 1.9 ng/mL and 2.1 ng/mL. In the other three samples, the concentrations were lower than 1 ng/mL. \\ \hline [PERSON] et al. (2021) [60] & GC-C-IRMS + 2D/3D-HPLC purification & Method validation \\ \hline [PERSON] et al. (2021) [61] & GC-C-IRMS & Method validation \\ \hline [PERSON] et al. (2021) [62] & GC-C-IRMS + 2D-HPLC purification & Method validation \\ \hline [PERSON] et al. (2021) [63] & GC-C-IRMS & Not clearly reported \\ \hline [PERSON] et al. (2022) [64] & Apatamers for in situ analysis, colorimetric testing, use of gold nanoparticles & Method validation \\ \hline [PERSON] et al. (2023) [65] & GC-MS/MS and GC-C-IRMS & After the consumption of boar, in two cases, the 19-NA concentrations were 2.8 ng/mL and 3.8 ng/mL. After the consumption of a supplement, the 19-NA concentration reached 3500 ng/mL. \\ \hline [PERSON] et al. (2023) [66] & Electrochemical sensors & Method validation \\ \hline \hline \end{tabular}
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[2023] & GC-MS: gas chromatography–mass spectrometry; LC-MS/MS: liquid chromatography with tandem mass spectrometry; GC-MS/MS: gas chromatography with tandem mass spectrometry; IAC: immunoadinfinity chromatography; GC-HRMS: gas chromatography/high-resolution mass spectrometry; GC-C-IRMS: gas chromatography/low-combustion/isotope ratio mass spectrometry; IDGC-HRMS: isotope dilution gas chromatography–high-resolution mass spectrometry; GCE: fullerene-modified glassy carbon electrode; SPME/LC-MS: solid-phase microextraction coupled to liquid chromatography–mass spectrometry. \\ \hline \hline \end{tabular}
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Table 1: _Cont._  
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**Authors** & **Mechanisms of Production and Metabolism** \\ \hline [PERSON] et al. (2001) [17] & The data suggested that the aromatization process contributes to nandrolone production and its metabolism, therefore reinforcing a long-held hypothesis that norandrogen synthesis is linked to the androgen-to-estrogen conversion. \\ \hline  & When nandrolone is administered, 19-norandrosterone is primarily excreted in a form conjugated to glucuronic acid, with almost no sulfate conjugates detectable in the samples. The levels of endogenous metabolites are minimal in comparison to the concentration of metabolites specifically associated with nandrolone administration. When produced endogenously, 19-norandrosterone is excreted in urine as a conjugate with both glucuronic acid and sulfuric acid. For endogenously produced 19-nonetiocholanolone, it is most often conjugated with glucuronic acid (approximately 84%), though a considerable proportion is also excreted as a sulfuric acid conjugate. These findings suggest that the presence of 19-NA and 19-NE can be attributed to endogenous production if sulfate conjugates are detected; however, their detection as glucuronide conjugates points specifically to \\  &