Short Answer

A Medical Review Officer, commonly called an MRO, is a licensed physician responsible for receiving laboratory drug test results and evaluating medical explanations for certain outcomes. The MRO reviews every non-negative laboratory result before it can be reported to an employer, decides whether a legitimate medical explanation accounts for the finding, and ultimately determines whether the result is verified as negative, positive, refused, cancelled, or another outcome under 49 CFR Part 40.

Where the MRO Fits in the Testing Process

Collection and laboratory analysis happen before the MRO ever gets involved. Once the laboratory reports a non-negative specimen, meaning it came back adulterated, substituted, positive, or invalid, the MRO's review begins. A negative result generally passes through to the employer without needing the same level of MRO intervention, since there is nothing to evaluate medically.

What the MRO Actually Reviews

The MRO reviews the laboratory paperwork and the chain of custody documentation on the CCF. For a non-negative result, the MRO typically contacts the employee to ask about any medications or medical conditions that could explain the laboratory finding. A verified test is the result of that process: a laboratory result that has undergone MRO review and reached a final determination.

The MRO's Role in Problem Cases

The MRO is also involved when a test does not go smoothly. If an employee cannot provide a sufficient urine specimen, the Designated Employer Representative (DER) must consult the MRO before directing the employee to obtain a further medical evaluation under 49 CFR § 40.193. The MRO also plays the central role in deciding whether a test must be cancelled outright under 49 CFR § 40.201, or cancelled unless a correctable flaw is fixed under 49 CFR § 40.203.

What the MRO Does Not Do

The MRO does not re-run the laboratory's chemistry and does not have unlimited authority to override a scientifically sound result simply because the employee disagrees with it. The MRO's authority is specifically about evaluating whether a legitimate medical explanation exists, and about applying the cancellation and correction rules in Subpart I, not about second-guessing accurate lab science on other grounds.

Applicable Regulations

• 49 CFR § 40.3 defines the MRO and the term "verified test."
• 49 CFR § 40.193 requires the DER to consult the MRO before directing an evaluation after an insufficient specimen.
• 49 CFR §§ 40.201 and 40.203 govern when the MRO must cancel a test outright or unless a flaw is corrected.

Professional Observation

In my experience, employees sometimes assume the MRO works for the employer, since the MRO's report ultimately goes to the DER. That framing misses the point. The MRO's job is to make an accurate medical determination based on the facts, not to advocate for either side.

Common Misconceptions

Misconception

The MRO can overturn a laboratory result for any reason the employee provides.

Reality

The MRO's authority to change a laboratory finding is limited to specific circumstances, such as a legitimate medical explanation or a procedural flaw under Subpart I. General disagreement with an accurate lab result is not, by itself, a basis to change the outcome.

Why the Confusion Occurs

Because the MRO is the person an employee talks to about a non-negative result, it can feel like the MRO has broad discretion, when in fact that discretion is narrowly defined by regulation.

Frequently Asked Questions

Can I call the MRO directly if I have a question about my result?

The MRO's office will generally reach out to the employee directly when review of a non-negative result requires it. Specific contact procedures can vary, so confirm the process with your employer's DER or the MRO's office handling your case.

Does the MRO tell my employer why I tested positive?

The MRO reports the verified result to the employer through the DER. What additional detail is shared depends on the circumstances and applicable confidentiality rules, and is best confirmed with the MRO directly.

Related Articles

• DOT Drug Testing Process
• How Laboratory Testing Works
• What Is the DOT Shy Bladder Procedure?
• What Is a Refusal to Test?

Primary Authorities/Sources

• 49 CFR § 40.3, Definitions
• 49 CFR § 40.193, Insufficient specimen
• 49 CFR § 40.201, Problems that always cancel a test
• 49 CFR § 40.203, Problems that cancel a test unless corrected

Need to Discuss a Test Result With an MRO?

If you believe a medical explanation applies to your result, raise it promptly with the MRO handling your case.

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