CERA Detection and Stability in Blood Versus Urine.

Erythropoietin receptor agonists (ERAs), including continuous erythropoietin receptor activators (CERAs), are potent blood doping substances used to enhance endurance performance by stimulating erythropoiesis. While traditionally detected through direct analysis of urine or serum samples using sarcosyl-polyacrylamide gel electrophoresis (SAR-PAGE) and western blotting, the slow urinary elimination of third-generation ERAs like CERA has shifted anti-doping strategies toward serum-based detection. This study compared the detectability and stability of CERA in urine and serum matrices and evaluated the added value of combining direct detection with hematological profiling. Using samples from a controlled CERA administration study and an authentic case example, we assessed CERA detection in serum, urine, and simulated dried blood spot (DBS) matrices (Tasso-M20). Additionally, we conducted stability experiments by incubating spiked matrices at 37°C for up to 72 h. Our results confirmed the superior stability and consistent detectability of CERA in serum and DBS compared with urine. Moreover, hematological alterations such as increased reticulocytes percentage flagged by the Athlete Biological Passport (ABP) supported targeted serum testing, leading to the successful detection of CERA. These findings highlight the importance of systematic blood collection for both direct and indirect detection strategies. Furthermore, DBS samples showed promising analytical performance and resistance to elevated temperature, suggesting their utility as minimally invasive alternatives in anti-doping programs. Overall, our study reinforces the relevance of blood matrices in the detection of CERA and advocates for the broader integration of blood-based strategies in targeting doping practices with ERAs.