Confirmation Test
A second, highly specific laboratory test (GC-MS or LC-MS/MS) performed after a positive initial immunoassay screen to confirm presence of a specific substance.
Key Facts
- Second-stage test after positive immunoassay screen
- Uses GC-MS or LC-MS/MS chromatography — highly specific
- Eliminates false positives from cross-reactive substances
- Required by 49 CFR Part 40 before any positive report
- Usually has lower cutoff than the initial screen
A confirmation test is the second analytical procedure performed on a specimen that tested positive or above the screening cutoff on the initial immunoassay. Confirmation uses gas chromatography–mass spectrometry (GC-MS) or liquid chromatography–tandem mass spectrometry (LC-MS/MS), which are highly specific and can identify exact substances and metabolites. Under 49 CFR Part 40, no drug test can be reported as positive without a confirmed result. Confirmation testing typically uses lower cutoff concentrations than the initial screen, ensuring that specimens at the borderline are accurately classified.
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