CLINICAL ISSUES ASSOCIATED WITH URINE TESTING OF SUBSTANCES OF ABUSE

Several factors may affect the validity and outcome of urine testing f or abused drugs such as amphetamines, barbiturates, benzodiazepines, c annabinoids, cocaine, ethanol, opiates, and phencyclidine. Urine is us ed for large-scale testing because acquisition of the sample is noninv asive and because most abused drugs can be detected in urine for a rea sonable duration after ingestion. Urine testing for drugs of abuse is a two-step process. In the first step, screening assays are used to id entify presumably positive specimens. Common screening tests are radio immunoassays, enzyme immunoassays, fluorescence polarization immunoass ay, and thin layer chromatography Since they may be subject to cross-r eactivity, once a possible positive sample has been identified by a pr eliminary test, a second more specific methodology, gas chromatography with mass spectrometry, is done to confirm the results. Knowledge of the pharmacology and pharmacokinetics of abused drugs affects selectio n and interpretation of test results.