A B sample is a urine or blood sample used in doping tests in professional sports to confirm or invalidate the presence of banned substances in the first sample, the A-sample. When samples are collected for drug testing, they are placed in two separate containers. The A sample is used to conduct the initial test. If sample A returns a positive result, the B sample can then be tested to verify the accuracy of the results. The use of A and B samples is an important safeguard because the consequences of an anti-doping violation can be career-ending for an elite athlete. When procedures used to test the A sample are flawed, the B sample provides an athlete with a chance to clear their name. The B sample is usually collected at the same time as the A sample and is stored in a separate container.