What does a Medical Review Officer (MRO) do?
A Medical Review Officer is a licensed physician with specific training in drug-testing regulations who reviews non-negative laboratory results, contacts the donor to identify any legitimate medical explanation (e.g., a prescription), and reports the verified result to the employer. Under 49 CFR Part 40 , every federally regulated test must be reviewed by a qualified MRO.
Why this two-step process exists
Screening ( Immunoassay ) is designed to be sensitive — it casts a wide net to flag samples that warrant further analysis. Sensitivity comes at the cost of specificity: immunoassays can produce false positives for benign exposures (poppy seeds, decongestants, some NSAIDs). The two-step structure exists to retain screening's speed and cost-effectiveness while ensuring a verified result is forensically defensible.
- Step 1 — screen by immunoassay. Result: negative or non-negative.
- Step 2 — confirm any non-negative by GC-MS or LC-MS/MS at a SAMHSA-certified lab. Result: negative or laboratory-positive.
- Step 3 — MRO review of any laboratory-positive with the donor. Result: verified positive, verified negative, or cancelled.
Confirmation testing
Confirmation testing uses GC-MS (gas chromatography–mass spectrometry) or LC-MS/MS (liquid chromatography–tandem mass spectrometry) , both of which separate analytes by mass and identify them with very high specificity. Confirmation cutoffs are lower than screening cutoffs because mass spectrometry is more precise. For example, the federal cannabinoid screening cutoff is 50 ng/mL of THC-COOH; the confirmation cutoff is 15 ng/mL.
The MRO interview
When a confirmation reports a laboratory-positive, the MRO contacts the donor for a verification interview. The MRO asks about prescriptions, over-the-counter medications, dietary factors, and any other potential explanations that could account for the result. The MRO does not contact the employer with the laboratory result during the review process; only the verified result is reported.
If the donor provides a legitimate medical explanation that the MRO is able to verify (typically by direct contact with the prescribing clinician and pharmacy), the MRO reports the result to the employer as negative with a verified prescription (or "consistent with prescribed therapy" in some formulations).
Possible MRO outcomes
- Verified negative — including laboratory positives with a verified legitimate medical explanation.
- Verified positive — laboratory positive without a verified legitimate medical explanation.
- Cancelled — fatal flaw in collection or chain of custody.
- Refusal to test — including some forms of adulteration or substitution.
- Dilute — dilute negative (under DOT may trigger retest at employer's discretion) or dilute positive (reported as positive).
The safety-concern report
Under 49 CFR Part 40, the MRO has authority to make a "safety concern" referral to the employer if the MRO has reasonable cause to believe a donor's continued performance of safety-sensitive functions could create a hazard, even where the test result is verified negative. This is a narrow safeguard, used sparingly.
MRO qualifications
A qualified MRO is a licensed physician (MD or DO) who has completed an MRO certification program — most commonly the American Association of Medical Review Officers (AAMRO) or the Medical Review Officer Certification Council (MROCC) — and maintains continuing education. DOT-regulated MROs have additional training requirements specified by Part 40, Subpart G.
Sources & references
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