Epitestosterone

Epitestosterone is a steroid that, based on its chemical structure, is classified as a stereoisomer of testosterone. In epitestosterone, the oxygen group (hydroxy group) is spatially oriented in the alpha position at carbon atom C-17, whereas testosterone has a 17β-hydroxy configuration. Epitestosterone is formed during synthesis in the human body from testosterone precursors and is physiologically inactive.

Epitestosterone serves as a reference steroid in testosterone testing (testosterone/epitestosterone ratio = T/E ratio). Testosterone cannot be converted into epitestosterone in the human body, which is why the T/E ratio increases when testosterone is administered.

Athletes whose urine samples show a T/E ratio greater than 4 are classified as atypical and undergo further testing to determine whether the elevated value is physiologically based or due to doping.