Kansas City, KS: Results of immunoassay urine screens – the most popular type of workplace drug tests – should always be considered presumptive until confirmed by a laboratory-based confirmation test (e.g., gas-chromatography-mass spectrometry testing), according to a review published in the journal Mayo Clinic Proceedings.
Investigators at the University of Kansas Medical Center conclude: “Immunoassays, which use antibodies to detect the presence of specific drugs or metabolites, are the most common method for the initial screening process. … However, these assays are not perfect. False positive results of immunoassays can lead to serious medical or socials consequences if the results are not confirmed by secondary analysis. … Also, urine drug screens do not provide information regarding the length of time since last [drug] ingestion, overall duration of [drug] abuse, or state of intoxication.”
Authors report that various prescription and over-the-counter medications may yield false positive drug test results on immunoassay tests, though these results are primarily limited to amphetamines, opioids, and phencyclidine (PCP).
For more information, please contact Paul Armentano, NORML Deputy Director, at: paul@norml.org. Full text of the study, “Urine drug screening: practical guide for clinicians,” is available online at: http://www.mayoclinicproceedings.com/Abstract.asp?AID=4580&Abst=Abstract&UID.