Urine Testing: The Basics

     Urine samples are usually tested for drugs by using a screening test followed by gas chromatography-mass spectroscopy (GCMS).  The screening test is normally an enzymatic method of analysis that determines if the “signal strength” is at or above a cut-off level.  These tests employ reagents that interact with several different but related compounds (e.g., metabolites) and measure the total “signal strength” of all those compounds. 

     GCMS should be able to identify both the parent drug and any metabolite(s).  If a parent drug is identified, the metabolite should also be present.  For example, if a urine sample is positive for methamphetamine, it should also be positive for amphetamine. 

     In order for a test result to be reported as positive the amount of a compound should equal or exceed the cut-off level.  If the cut-off limit for the GCMS is not met, the result should be reported as negative.   In other words, sound science dictates that reports reading “lower than the lowest calibrator” should not be reported as positive.

     One final word about metabolites: Most metabolites are less psychoactive than the parent drug or are inactive, which means that they have no impact on the person.  If only an inactive metabolite such as carboxy THC is found in a urine sample, the metabolite did not affect driving. 

Written by Allen Trapp who is board certified by the National College for DUI Defense and the author of Georgia DUI Survival Guide Visit Website Written by Allen Trapp who is board certified by the National College for DUI Defense and the author of Georgia DUI Survival Guide Visit Website

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