• DOT · Federal
  • HHS · Federal
  • Urine
  • Lab confirmation

What Is a Medical Review Officer (MRO)?

Short answer

A Medical Review Officer is a licensed physician who reviews drug test results before your employer sees them. The MRO checks the paperwork for errors, and where a laboratory reports a positive, contacts you first so you can explain a legitimate medical reason. Only after that review does a result get reported — and the MRO reports the outcome, not your medical information.

Last verified 17 Aug 2026 Reviewed with Dr. Matthew Nuesse, DOT Certified Medical Examiner

What matters most

  • An MRO is a licensed physician, independent of the laboratory that ran the test.
  • A laboratory result is not final until the MRO has verified it.
  • The MRO must give you the chance to explain a legitimate medical explanation before reporting a positive.
  • The MRO tells your employer the outcome, not your medical history or your medications.
  • The MRO must inform you of your right to have the split sample tested at a second laboratory.

What an MRO is

A Medical Review Officer is a licensed physician with specific training in the drug testing process, acting independently of the laboratory that analysed your sample. The role exists because a laboratory can tell you what was in a sample but not whether there is a lawful explanation for it, and because the paperwork itself can fail in ways that should invalidate a result Source 1DOT ODAPC49 CFR Part 40 — section navigator and Q&As — checked 17 Aug 2026Source 2eCFR49 CFR Part 40 — Procedures for Transportation Workplace Drug and Alcohol Testing Programs — checked 17 Aug 2026.

What the MRO does with your result

Federal (DOT): Every result passes through the MRO before it reaches your employer. The MRO reviews the custody and control form and the laboratory report, looking for problems that cannot be corrected — an unsealed specimen, a missing signature, a break in the chain of custody. Some flaws are fatal to the test and the result is cancelled Source 1DOT ODAPC49 CFR Part 40 — section navigator and Q&As — checked 17 Aug 2026Source 2eCFR49 CFR Part 40 — Procedures for Transportation Workplace Drug and Alcohol Testing Programs — checked 17 Aug 2026.

Federal (HHS): Federal civilian employee programmes use the same review structure, under the Department of Health and Human Services guidelines rather than the DOT rules Source 3SAMHSAFederal Workplace Drug Testing FAQs — checked 17 Aug 2026.

The verification interview

This is the part most people do not know exists. Where the laboratory reports a positive, the MRO has to try to reach you before reporting anything to your employer, so that you can offer a legitimate medical explanation for the result Source 1DOT ODAPC49 CFR Part 40 — section navigator and Q&As — checked 17 Aug 2026Source 2eCFR49 CFR Part 40 — Procedures for Transportation Workplace Drug and Alcohol Testing Programs — checked 17 Aug 2026.

A valid prescription for a medication that accounts for the finding is the usual example. This conversation is short and practical if you have the prescribing details to hand — who prescribed it, when, and for what. It is worth answering the call: the MRO is required to attempt contact, and an unreturned message does not pause the process indefinitely.

The MRO must also tell you that you may request the split portion of your sample be tested at a second certified laboratory Source 1DOT ODAPC49 CFR Part 40 — section navigator and Q&As — checked 17 Aug 2026Source 2eCFR49 CFR Part 40 — Procedures for Transportation Workplace Drug and Alcohol Testing Programs — checked 17 Aug 2026.

What the MRO does not do

The MRO is not your doctor and is not deciding anything about your job. They do not pass your medical history or your medication list to your employer — what gets reported is the verified outcome of the test. They do not decide whether you are disciplined, and they do not run the return-to-duty process, which is a separate role.

Employer policy: What your employer does with a verified result is governed by its own policy and any collective agreement, not by the MRO and not by the testing regulation.

How the process runs

  1. Paperwork review

    The MRO checks the custody and control form and the laboratory report for errors serious enough to invalidate the test.

  2. Contact attempt

    Where the laboratory has reported a positive, adulterated or substituted result, the MRO attempts to reach you directly before reporting anything.

  3. Verification interview

    You get the opportunity to offer a legitimate medical explanation. If you have a valid prescription that accounts for the result, this is where it is raised.

  4. Verified result

    The MRO reports a verified outcome to your employer and tells you about your right to have the split sample tested.

What this means for you

If an MRO contacts you, that call is your opening, not a formality — it is the designed point in the process where a lawful explanation can change the outcome. Take it, and have prescribing details ready if a medication could account for the result. If you are told a result has been verified, ask about the split sample: the right to have the second bottle tested is time-limited, and the clock starts when you are notified.

Rules differ by state and employer. This section describes federal requirements. Your state law or your employer’s written policy may add rules on top of them.

When the answer changes

A non-DOT test your employer runs on its own account does not have to involve an MRO at all, and many do not. If nobody has offered you a verification interview, that is a strong hint you are in a private programme rather than a federal one — worth clarifying before you assume which rules apply to you.

Dr. Matthew Nuesse
Medical review

Dr. Matthew Nuesse

DOT Certified Medical Examiner

Dr. Matthew Nuesse is a DOT Certified Medical Examiner who reviews Exploro's drug testing guides for medical and procedural accuracy.

Common questions

No. A sample that screens positive goes on to a second, more specific confirmatory test, and the result is then reviewed by a Medical Review Officer. The MRO must give you the chance to explain a legitimate medical reason before reporting the result to your employer.

Source:49 CFR Part 40 (ODAPC), 49 CFR Part 40 (eCFR)

Yes. Every DOT collection splits your sample into two bottles. If the Medical Review Officer reports a positive, refusal, adulterated or substituted result, you have 72 hours from being told to request that the second bottle be tested at a different certified laboratory. The MRO has to tell you about this right.

Source:49 CFR Part 40 (ODAPC), 49 CFR Part 40 (eCFR)

Not under the federal rules. 49 CFR Part 40 governs how you are tested and removed from safety-sensitive duties — it says nothing about your employment. Whether you keep your job depends on your employer's written policy and any collective agreement.

Source:49 CFR Part 40 (ODAPC), 49 CFR Part 40 (eCFR)

Official sources

Every factual claim above is drawn from these sources. Each was opened and checked on the date shown. Where a rule differs between agencies, the source that governs is named in the text.

  1. DOT ODAPC · 49 CFR Part 40 (ODAPC)

    49 CFR Part 40 — section navigator and Q&As

    Checked 17 Aug 2026
    View official source ↗ (opens in a new tab)
  2. eCFR · 49 CFR Part 40 (eCFR)

    49 CFR Part 40 — Procedures for Transportation Workplace Drug and Alcohol Testing Programs

    Checked 17 Aug 2026
    View official source ↗ (opens in a new tab)
  3. SAMHSA · SAMHSA — Federal workplace FAQs

    Federal Workplace Drug Testing FAQs

    Checked 17 Aug 2026
    View official source ↗ (opens in a new tab)