<P> Laboratory - based drug testing is done in two steps . The first step is the screening test, which is an immunoassay based test applied to all samples . The second step, known as the confirmation test, is usually undertaken by a laboratory using highly specific chromatographic techniques and only applied to samples that test positive during the screening test . Screening tests are usually done by immunoassay (EMIT, ELISA, and RIA are the most common). A "dipstick" drug testing method which could provide screening test capabilities to field investigators has been developed at the University of Illinois . </P> <P> After a suspected positive sample is detected during screening, the sample is tested using a confirmation test . Samples that are negative on the screening test are discarded and reported as negative . The confirmation test in most laboratories (and all SAMHSA certified labs) is performed using mass spectrometry, and is precise but expensive . False positive samples from the screening test will almost always be negative on the confirmation test . Samples testing positive during both screening and confirmation tests are reported as positive to the entity that ordered the test . Most laboratories save positive samples for some period of months or years in the event of a disputed result or lawsuit . For workplace drug testing, a positive result is generally not confirmed without a review by a Medical Review Officer who will normally interview the subject of the drug test . </P> <P> Urine drug test kits are available as on - site tests, or laboratory analysis . Urinalysis is the most common test type and used by federally mandated drug testing programs and is considered the Gold Standard of drug testing . Urine based tests have been upheld in most courts for more than 30 years . However, urinalysis conducted by the Department of Defense has been challenged for reliability of testing the metabolite of cocaine . There are two associated metabolites of cocaine, benzoylecgonine (BZ) and ecgonine methyl ester (EME), the first (BZ) is created by the presence of cocaine in an aqeous solution with a pH greater than 7.0, while the second (EME) results from the actual human metabolic process . The presence of EME confirms actual ingestion of cocaine by a human being, while the presence of BZ is indicative only . BZ without EME is evidence of sample contamination, however, the US Department of Defense has chosen not to test for EME in its urinalysis program . </P> <P> A number of different analyses (defined as the unknown substance being tested for) are available on Urine Drug Screens . </P>

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