Role of the laboratory in the evaluation of suspected drug abuse.

Despite the high incidence of substance abuse, it remains a common cause of misdiagnosis. In patients who have abused or who are currently abusing drugs, symptoms of a psychiatric illness may be mimicked by either the drug's presence or absence. The laboratory can aid in making a differential diagnosis and eliminating drugs from active consideration as a cause of psychosis, depression, mania, and personality changes. Treatment planning and prevention of serious medical consequences often rest on the accuracy of the admission drug screen. Testing is widely used to assess improvement in substance abuse in both inpatient and outpatient settings. In occupational settings, testing has been used as an early indicator that a problem exists and as a successful prevention tool. The appropriate use of analytic technology in drug abuse testing requires an understanding of available test methodologies. These include drug screens by thin-layer chromatography, comprehensive testing using enzyme immunoassay, and computer-assisted gas chromatography-mass spectrometry (GC-MS). Testing for specific drugs considered likely causes or precipitants of "psychiatric" complaints is available with enzyme assays, radioimmunoassay, or definitive forensic-quality testing using GC-MS.