The most commonly used AAS in medicine are testosterone and its various esters (but most commonly testosterone undecanoate , testosterone enanthate , testosterone cypionate , and testosterone propionate ),  nandrolone esters (most commonly nandrolone decanoate and nandrolone phenylpropionate ), stanozolol , and metandienone (methandrostenolone).  Others also available and used commonly but to a lesser extent include methyltestosterone , oxandrolone , mesterolone , and oxymetholone , as well as drostanolone propionate , metenolone (methylandrostenolone), and fluoxymesterone .  Dihydrotestosterone (DHT; androstanolone, stanolone) and its esters are also notable, although they are not widely used in medicine.  Boldenone undecylenate and trenbolone acetate are used in veterinary medicine . 
In the US, the most common form of steroid testing is more sophisticated than any of these three. It’s called antibody-antigen based radioimmunoassay. This term may sound complicated, but simply put, it uses a series of antibodies to seek out and measure the concentrations of antigens in the body. Hormones like anabolic steroids are considered antigens for this purpose, and the test is surprisingly accurate. If an individual tests positive, though, chromatography is performed. This process passes either blood or urine through a very specific medium to measure the rates at which different components move. It is even more accurate than the radioimmunoassay procedure, and is used mostly by anti-doping agencies.