A drug test is a technical analysis of a biological specimen, for example urine, hair, blood, breath, sweat, and/or oral fluid/saliva—to determine the presence or absence of specified parent drugs or their metabolites. Major applications of drug testing include detection of the presence of performance enhancing steroids in sport, employers and parole/probation officers screening for drugs prohibited by law and police officers testing for the presence and concentration of alcohol (ethanol) in the blood commonly referred to as BAC. BAC tests are typically administered via a breathalyzer while urinalysis is used for the vast majority of drug testing in sports and the workplace. Numerous other methods with varying degrees of accuracy, sensitivity, and detection periods exist.
Read article on Wikipedia