Specific procedures for detecting anabolic steroids in athletes' urine have been developed at International Olympic Committee (IOC) authorized laboratories. Gas-chromatography combined with mass spectrometry is the method of choice for doing this (GC-MS). Other techniques such as high performance liquid chromatography (HPLC), enzyme-linked immunosorbent assay (ELISA) and radioimmunoassay (RIA) are also used. In order to obtain a positive result, drugs must be administered for a period longer than seven days. After this time, they will appear in the urine. The only way to prove that an athlete did not use steroids is by testing his or her blood sample. If there are no banned substances present, it can be concluded that the athlete did not use drugs. Some labs may also offer a "retest" option so that if an athlete's sample tests negative once, he or she does not have any drugs in their system, even if they stopped using them earlier that day, week, or month. The retest process involves taking another sample one to three months after the first test. If an athlete refuses to give consent for a steroid drug test, then it cannot be done. It is important for athletes to understand the nature of these tests and the consequences of failing them.