How Does a Laboratory Confirm a Positive DOT Drug Test?

A laboratory confirms a positive DOT drug test by running a second, different test on a separate portion of the specimen. Under 49 CFR 40.3, an initial drug test is the first test used to differentiate a negative specimen from one that requires further testing. A confirmatory drug test is a second analytical procedure performed on a different aliquot of the original specimen to identify and quantify a specific drug or drug metabolite.

Under 49 CFR 40.85(b), if the initial urine result is below the cutoff concentration, the laboratory reports it as negative. If it is at or above the cutoff, the laboratory conducts a confirmation test. Under 40.85(c), a confirmation result below the cutoff is reported as negative, and a result at or above the cutoff is reported as confirmed positive. The cutoffs are covered in What Are the Cutoff Levels for a DOT Urine Drug Test? and What Are the Cutoff Levels for a DOT Oral Fluid Drug Test?.

Under 49 CFR 40.97(b)(2), a positive result is reported with the drugs or metabolites noted and numerical values for each. Under 40.97(f)(1), the laboratory provides quantitative values for confirmed positive results to the MRO.

Under 40.97(c), the result goes directly, and only, to the Medical Review Officer (MRO), and the laboratory releases it after review by its certifying scientist. Under the 40.3 definition of a verified test, a laboratory result becomes verified only after the MRO's review and final determination. Split specimen testing is covered in How Does a Split Specimen Test Work after a Positive DOT Drug Test?.

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