# Exogenous Versus Endogenous Nandrolone in Doping Investigations: A Systematic Literature Review
## 4 Discussion
Additional factors were investigated for their potential effects on 19-nortestosterone metabolism, including dietary habits, the use of steroid-based medications, and drugs acting as masking agents for the main metabolites 19-NA and 19-NE. An increased presence of nandrolone metabolites in urine can create serious challenges for doping control measures, where the accepted limit is set at 2 ng/mL. For example, consuming wild boar meat has been shown to produce detectable levels of 19-NA and 19-NE in urine, which could result in disqualification for an athlete under doping regulations [65]. Similarly, certain dietary supplements containing steroids--sometimes available as over-the-counter products--can raise urinary levels of 19-NA and 19-NE [14; 29]. Medications prescribed to manage menstrual cycle disorders, including those containing nortestosterone, have also been found to potentially increase levels of nandrolone metabolites in urine [41]. Additionally, certain types of eye medications (ophthalmic drugs) can produce similar effects [33; 43]. The use of these products may unintentionally lead to elevated concentrations of nandrolone metabolites in an athlete's urine, thereby heightening the likelihood of a positive result in doping tests. This unintended increase in metabolite levels could pose a serious risk for athletes, as it may result in them being flagged for substances that they did not intentionally consume as performance enhancers. What has been discussed so far is reflected in the concentrations found in the samples analyzed by the various studies. In fact, only trace amounts of 19-NA were found in most cases. However, significant increases were found following the consumption of wild boar meat. Regarding exercise, it was found that 19-NA levels generally remained low, suggesting that while exercise might influence some metabolic pathways, it does not significantly elevate nandrolone secretion. In conclusion, these results collectively underscore the complexity of analyzing nandrolone and its metabolites in urine samples. Gas chromatography and liquid chromatography, when combined with mass spectrometry, have firmly established themselves as the preferred analytical methods for detecting nandrolone and its metabolites in urine. Specifically, techniques such as GC/MS or GC/MS/MS are frequently employed for the precise identification of these substances. Although LC/MS or LC/MS/MS methods are also utilized, they are less commonly used as stand-alone techniques for this purpose. The most significant advancement in this field is the application of GC-C-IRMS, which stands out as the only technique capable of accurately differentiating between the endogenous (naturally produced) and exogenous (externally introduced) forms of nandrolone [32]. This differentiation is based on detecting abnormal carbon-13 (13C) isotope values of 19-NA in urine. Values outside the typical endogenous steroid range, approximately between \(-17\%\) and \(-25\%\), signal the intake of synthetic nandrolone [49; 55]. Therefore, GC-C-IRMS offers a high degree of reliability for anti-doping testing by identifying synthetic sources of nandrolone with precision [57]. Moreover, the steps taken in sample pretreatment are crucial for ensuring the accuracy of GC-C-IRMS results, as they must prevent any potential contamination. Effective purification techniques include solid-phase extraction (SPE), liquid/liquid extraction, and immunoaffinity chromatography (IAC), often used after enzymatic hydrolysis to prepare the sample. Additionally, high-performance liquid chromatography (HPLC) separation and fractionation serve as vital pre-analytical purification steps, ensuring that the sample is sufficiently purified for reliable analysis. Together, these techniques strengthen the detection capabilities in anti-doping control by enabling clear differentiation between naturally occurring and synthetic randomone sources.