Urine testing in the detection of drugs of abuse.

It is vital that physicians are alert to signs and symptoms of arcane drug use by their patients and be prepared to order appropriate laboratory tests that will assist in differentiating problems associated with drug use from those stemming from other causes. Physicians should be familiar with the advantages and disadvantages of the more common screening procedures for drugs of abuse. As a result of recent technical improvements in the instrumentation and reagents used to test for drugs of abuse in urine specimens, these tests, properly performed, are highly accurate for cannabinoids and cocaine, the two most frequently abused drugs; a positive test for opiates and amphetamines is much less specific. By using a two-tiered system of confirmation of positive screening tests that employs techniques such as gas chromatography with mass spectrometry, the incidence of false-positive results is minimal. This article presents guidelines for determining when to order a drug screen; a lexicon of terms commonly used in discussions of screening tests; a description of the advantages, disadvantages, technique, and means of interpreting the more widely used tests; and a section on each of the most frequently abused drugs that describes common errors in test interpretation.