For decades, the class of anabolic androgenic steroids has represented the most                    frequently detected doping agents in athletes’ urine samples. Roughly                    50% of all adverse analytical findings per year can be attributed to                    anabolic androgenic steroids, of which about 2/3 are synthetic exogenous                    steroids, where a qualitative analytical approach is sufficient for routine                    doping controls. For the remaining 1/3 of findings, caused by endogenous                    steroid-derived analytical test results, a more sophisticated quantitative                    approach is required, as their sheer presence in urine cannot be directly linked                    to an illicit administration. Here, the determination of urinary concentrations                    and concentration ratios proved to be a suitable tool to identify abnormal                    steroid profiles. Due to the large inter-individual variability of both                    concentrations and ratios, population-based thresholds demonstrated to be of                    limited practicability, leading to the introduction of the steroidal module of                    the Athlete Biological Passport. The passport enabled the generation of                    athlete-specific individual reference ranges for steroid profile parameters.                    Besides an increase in sensitivity, several other aspects like sample                    substitution or numerous confounding factors affecting the steroid profile are                    addressed by the Athlete Biological Passport-based approach. This narrative                    review provides a comprehensive overview on current prospects, supporting                    professionals in sports drug testing and steroid physiology.