What’s the difference between a direct and indirect marker of doping?
When the laboratory method detects the presence of a prohibited substance (or its metabolites) in the blood or urine of an athlete, it is known as a direct marker of doping. Indirect markers are biological variables that can be measured and are related to the effect of the prohibited substance without necessarily directly identifying the administered substance or method. Traditionally, detection of doping in sport has relied on direct markers. However, in 2009, the World Anti-Doping Agency approved the Hematological Model of the Athlete Biological Passport (ABP) which relies on measuring indirect markers over time to detect possible doping.
The ABP consists of a Hematological Module and a Steroidal Module. The Hematological Module monitors variables such as hemoglobin, reticulocyte count, hematocrit, and red blood cell count. The objective of measuring these indirect hematological markers is to identify possible Erythropoiesis Stimulating Agents (ESAs) or homologous blood transfusions. The Steroidal Module, which came in to effect in 2014, monitors variables such as Testosterone, Epitestosterone, and Androsterone. The objective of measuring these biomarkers is to identify the abuse of exogenous steroids. The Hematological Module and Steroidal Module complement each other and can be used to identify potential athletes for further target testing as well as to assist in the detection of anti-doping rule violations. For both models, other measurements are being researched for addition to the profile in order to make the indirect tests better able to detect abuse of exogenous substances and methods.
When measuring biomarkers, the window of detection can be extended due to a prolonged biological response, so a whole range of substances may be tackled in an indirect manner.