RNA biomarkers in antidoping.

The detection of doping in sport has historically relied on the direct identification of exogenous substances or their metabolites in urine and blood. While effective for xenobiotics, this strategy is not always applicable for detection of pseudo-endogenous compounds such as testosterone or recombinant human erythropoietin (rhEPO), where endogenous production adds a layer of complexity to interpretation. To overcome these limitations, the Athlete Biological Passport (ABP) was developed, shifting the focus toward individualized, longitudinal monitoring of biological responses. The ABP currently includes hematological, steroidal, and endocrine modules, each targeting distinct classes of prohibited substances and methods. Despite its improved sensitivity, the ABP remains constrained by a limited repertoire of biomarkers, susceptibility to confounding factors, and the sophistication of emerging doping strategies. Recent advances in molecular biology have highlighted RNA-based biomarkers such as messenger RNAs (mRNAs) and microRNAs (miRNAs) as promising complementary tools for ABP. Blood transcriptomics provides sensitive indicators of erythropoietic stimulation and blood manipulation, with genes such as ALAS2 and CA1 that have shown strong responses to rhEPO and transfusion. The introduction of dried blood spots (DBS) as sample matrix has further enhanced feasibility by simplifying collection, storage, and transport, while preserving RNA integrity. However, before integration into the ABP, inter-laboratory harmonization and validation, quality control systems, and regulatory framework are essential. Beyond human testing, RNA biomarkers also demonstrate translational potential in equine anti-doping and clinical contexts such as treatment of anemia. Together, these developments underline the potential of RNA profiling to expand the ABP framework, improve sensitivity, and strengthen global anti-doping programs through a next generation of biomarkers.