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

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Screening: Point of Care Drug Tests

Point of care (POC) drug testing is performed outside the clinical laboratory in a location close to where the patient is receiving care.
The principle of POC drug testing devices is based on competition between dye conjugated antibodies binding to drug present in the urine sample and dyed conjugated antibodies binding to drug that is bound to a porous membrane. If drug is not present, dyed antibodies bind the drug bound to the membrane and a colored line appears in the test window. When the concentration of drug in the urine sample equals or exceeds the cutoff concentration for the particular POC device, the drug in the sample is saturated with antibody, preventing the antibody from binding to the drug that is bound to the membrane. No line is formed in the test window, indicating a positive result. This seems counterintuitive and has been confusing to users of these devices. However, POC devices that operate on a more logical principle and produce a color for positive results and no color for negative results have been developed and are in use in some facilities today.
Despite the obvious advantage of rapid results, there are disadvantages to POC testing compared to laboratory based immunoassays. POC testing is typically performed by non-laboratory personnel and is more subjective in nature.
Physicians should carefully evaluate the value of POC devices before adapting them for routine use.