Analysis of a person's urine can disclose many details about that person's private life other than drug use. It can tell an employer whether an employee or job applicant is being treated for a heart condition, depression, epilepsy or diabetes. It can also reveal whether an employee is pregnant. The drug screens used by most companies are not reliable. These tests yield false positive results at least 10 percent, and possibly as much as 30 percent, of the time.
Experts concede that the tests are unreliable.
Although more accurate tests are available, they are expensive and infrequently used. And even the more accurate tests can yield inaccurate results due to laboratory error. A survey by the National Institute of Drug Abuse, a government agency, found that 20 percent of the labs surveyed mistakenly reported the presence of illegal drugs in drug-free urine samples. Unreliability also stems from the tendency of drug screens to confuse similar chemical compounds. For example, codeine and Vicks Formula 44-M have been known to produce positive results for heroin, Advil for marijuana, and Nyquil for amphetamines.