Urine Drug Testing: Immunoassay vs. Laboratory Testing

Immunoassay (also known as “point-of-care” or “office collection”) testing should always be considered the first step in a sound UDT program. This type of testing quickly and efficiently identifies specific drugs or metabolites utilizing antibodies. It is important to note, however, that immunoassays are best suited as screening tests; their diagnostic inaccuracy and the risk of false-positive or false-negative results render them subject to possible misinterpretation.

Urine drug testing companies have their own sophisticated laboratories which perform UDT with greater accuracy than that provided by in-office immunoassay screening. When an immunoassay test is inconsistent (i.e. indicating the presence of a prescription or illicit drug that should not be in the sample, or, conversely, not containing evidence of a medication that should be in the sample), more expensive and accurate confirmation testing should be conducted.  According to a large retrospective study, between 3 and 5% of screening results should be sent for confirmation testing.

From an ethical perspective, confirmation testing should be performed on all inconsistent immunoassays, as the repercussions of a false-positive screen can be dramatic.  Confirmation testing was typically conducted through gas chromatography/mass spectrometry (GC/MS), although recent advances in technologies such as liquid chromatography-tandem mass spectrometry (LC-MS/MS) are beginning to bring about a paradigmatic revision in laboratory practices.  Importantly, the validity for extreme accuracy of both of these types of testing has been established.

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