What Is an MRO?
An MRO — Medical Review Officer — is a licensed physician who reviews all DOT drug test results before they reach your employer. No result, positive or negative, goes to an employer without first passing through the MRO. For negative results this is a quick administrative review. For non-negative results the MRO must contact you directly for a private interview before reporting anything.
Key rule: Your employer cannot see any test result until after the MRO completes their review. Only the final verified result is reported — not the lab's initial finding.
Step-by-Step Timeline
Why MRO Review Takes Longer Than Expected
- GC/MS confirmatory testing — adds 1–3 days to the initial screen timeline
- Specimen validity testing — if the specimen is flagged as dilute, substituted, or adulterated, additional analysis is required
- MRO cannot reach the donor — the single most common delay; the MRO must make multiple attempts before escalating
- Medical records requested — if the donor claims a prescription or medical condition, the MRO may request documentation from the prescribing physician
- Insufficient specimen volume — if Bottle A volume is too low for testing, the specimen may be reported as a cancelled test and a new collection ordered
- Split specimen request — if you request Bottle B testing within 72 hours of the MRO notification, an additional 3–7 days are added
The Split Specimen Request Window
If the MRO notifies you of a verified positive, you have 72 hours from that notification to request that Bottle B be tested at a second SAMHSA-certified laboratory at your own expense. This is your right under 49 CFR Part 40. The split specimen result typically comes back within 3–7 additional business days. If Bottle B also confirms positive, the original result stands.
Does the Employer See Results Before MRO Review?
No. Under DOT regulations, the employer only receives the MRO-verified final result. The lab never contacts the employer directly. The MRO's review is the firewall that ensures a driver with a legitimate medical explanation for a non-negative result is not wrongfully reported as positive.
Frequently Asked Questions
How long does MRO review take for a DOT drug test?
A negative DOT drug test result typically clears MRO review in 2–4 business days from collection. A non-negative result that requires a donor interview takes 5–10 business days, sometimes longer if the MRO has difficulty reaching the donor or if medical records are needed.
Can I work while waiting for MRO review?
For a pre-employment test, most employers wait for a negative result before allowing a new hire to perform safety-sensitive duties. For a random test during employment, you typically continue working until the MRO reports a result. If the MRO reports a verified positive, you are removed from safety-sensitive duties immediately.
Why is my MRO review taking longer than expected?
Common reasons: the MRO is trying to reach you for a donor interview (answer all calls from unknown numbers), GC/MS confirmatory testing is in progress, specimen validity testing flagged an issue, or medical records were requested from your doctor.
What happens if the MRO cannot reach me?
If the MRO cannot reach you after multiple attempts, they contact your employer's Designated Employer Representative (DER) to help facilitate contact. If you still cannot be reached, the MRO may verify the result as positive by default. Always answer unknown numbers when you have recently given a DOT drug test.
Does the employer see the result before MRO review is complete?
No. The employer only receives the final verified result after the MRO completes their review. The employer never sees the lab's initial non-negative result directly.
What is a split specimen and how does it affect the timeline?
Every DOT urine specimen is split into two at collection — Bottle A (tested first) and Bottle B (held). If Bottle A is non-negative, you have 72 hours to request that Bottle B be tested at a different certified lab. This split specimen test typically adds 3–7 days to the total timeline.
Reviewed by Chantal Gabriel, MD
Medical Director, WorkOccMed Medical Group, PLLC – FMCSA-Certified Medical Examiner. This guide is reviewed by a certified medical examiner for accuracy.