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The page below is a sample from the LabCE course . Access the complete course and earn ASCLS P.A.C.E.-approved continuing education credits by subscribing online.

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Drug Testing

Urine is the most common body fluid chosen for drug testing in clinical toxicology laboratories. It is much less expensive to analyze than blood, hair, sweat, and saliva. It is easily and noninvasively collected. It is also a very clean matrix in comparison to blood, which is loaded with proteins and lipids that can interfere with detection of the analyte. There is a relatively long window of detection in urine (1 to 3 days). In addition, there is an abundance of assay information available, and it is the most extensively validated matrix for drug testing.
Unlike forensic drug testing, where there is a rigorous chain of custody and the results can be used as evidence in a criminal court, clinical drug testing is used in a therapeutic setting for diagnosis and treatment.
There are many reasons why a physician would order a urine drug test:
  • To aid the emergency room doctor in diagnosis
  • To make an initial diagnosis of drug abuse or addiction
  • To assist in medication adherence
  • To monitor compliance in addiction medicine
  • To monitor compliance in a pain management program
Urine drug testing is used ultimately to improve patient care. Therefore, interpretation of the results is very important. Just like any other diagnostic test, an inappropriate interpretation can adversely affect patient care. The physician should consult with the laboratory director or toxicologist when uncertain of the interpretation of the results of a urine drug test.