What Is a Drug Test / Drug Screen?
Evidence-based answer reviewed against SAMHSA cutoffs and FDA assay documentation · Updated August 2026
Quick answer: A drug test analyzes a biological specimen (urine, oral fluid, hair, blood, sweat) to detect drug use. A 'screen' usually means the rapid immunoassay step; confirmed results require laboratory mass spectrometry.
Two-step science: screen then confirm
Step 1 — immunoassay screen: antibodies bind large retailers drugs above cutoff concentrations. Fast (minutes onsite, hours at lab), cheap, but cross-reactive — this is where false positives live.
Step 2 — GC–MS or LC–MS/MS confirmation: mass spectrometry uniquely identifies molecules. Every federally regulated positive MUST be confirmed; confirmation false-positives are vanishingly rare.
Who reports your result: the MRO
In regulated programs, a certified Medical Review Officer — a physician — reviews positives, interviews you about prescriptions, and issues the final verified result. Legitimate prescriptions become negatives-with-note at this stage.
Panel sizes explained
Panels count DRUGS tested: 5-panel (federal standard), 10-panel (common general workforce), 12-panel (adds oxy/buprenorphine/fentanyl-era analytes), 14–17-panel cups layer specialty strips. Bigger isn't automatically stricter — relevance depends on what your employer orders.
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Do prescriptions count against me?
No — verified prescriptions report as negative through the Medical Review Officer. Declare medications at collection and answer the follow-up call.
Sources & further reading
- SAMHSA — Mandatory Guidelines for Federal Workplace Drug Testing Programs (cutoffs, MRO process)
- DOT — 49 CFR Part 40 procedures for transportation workplace testing
- Brahm NC et al., Mayo Clinic Proceedings 2008;83(1):66–76 — false-positive cross-reactivity reference
- FDA — drug-of-abuse test device labeling (detection window conventions)