Drugs of abuse testing in a psychiatric outpatient service.

Drug testing of patients in a psychiatric outpatient service is an effective way to identify patients who relapse into renewed use of drugs of abuse and in monitoring the effectiveness of ongoing medical and psychological therapy. Most of this testing involves the analysis of urine specimens with immunoassays. Hair testing affords an alternative specimen matrix that is easy to obtain and not readily adulterated and offers the advantage of a wider surveillance window. Hair analysis is technically demanding, and the possibility of false-positives caused by environmental contamination renders it a controversial alternative. Sweat and saliva are potentially useful testing matrices, but their usefulness in clinical practice must await validation by additional clinical and laboratory experience. The correct interpretation of drug test results is predicated on knowing the performance characteristics of the analytical method, route of administration, and pharmacokinetics of the drug. All questionable positive results need confirmation testing to verify true positivity.