A Medical Review Officer (MRO) is a licensed physician who serves as an independent, impartial evaluator and advocate for the accuracy and integrity of the drug testing process. Under 49 CFR Part 40, the MRO is responsible for reviewing all laboratory results generated by an employer’s drug testing program and determining whether a legitimate medical explanation exists for certain results before reporting them to the employer.
The MRO performs three core functions in the drug testing process:
Quality assurance. The MRO reviews the drug testing procedure for every sample under their review, including the chain-of-custody documentation, laboratory analysis methodology, and procedural compliance. If errors exist that affect the integrity of the result, the MRO has the authority to cancel the test.
Medical determination. The MRO evaluates whether there is a legitimate medical explanation for any laboratory-confirmed positive, adulterated, substituted, or invalid result. This requires direct contact with the donor for a private medical interview before any results are reported to the employer.
Result flow and confidentiality. The MRO ensures the timely reporting of verified results to the employer’s Designated Employer Representative (DER) while protecting the confidentiality of all drug testing information throughout the process.
These three functions exist to protect both the employer and the employee. No employer receives a laboratory result before the MRO review is complete. This is not optional under DOT regulations and cannot be bypassed for any reason.
Role 1: Quality Assurance of the Drug Testing Process
The MRO’s quality assurance function begins when the SAMHSA-certified laboratory transmits results. The MRO reviews the federal custody and control form (CCF) for completeness and procedural accuracy alongside every result, not only for non-negative outcomes.
Under 49 CFR Part 40.199, certain CCF errors are classified as fatal flaws that require automatic test cancellation regardless of the laboratory finding. These include a specimen ID on the urine vials that does not match the paperwork, evidence of specimen leakage or insufficient quantity during transit, absence of the collector’s signature or printed name, and a discrepancy in appearance between specimen bottles. Other errors can be corrected through a memorandum from the collector. When a test is canceled due to a fatal flaw, the MRO reports the cancellation to the DER without a drug result, and a recollection must be arranged.
This review function means the MRO is the final check on procedural integrity before any result reaches the employer. A collection that follows every protocol correctly produces a clean CCF review. Errors at the collection stage that go unresolved become visible at the MRO review stage, which is one practical reason why working with qualified collectors matters. For a detailed walkthrough of the collection and chain-of-custody process, see our drug screen process guide.
Role 2: Medical Determination for Non-Negative Results
When the laboratory reports a positive, adulterated, substituted, or invalid result, the MRO must attempt direct personal contact with the donor before reporting any outcome to the employer. This is the medical determination function, and it is the most consequential step in the process for both employers and employees.
The MRO contacts the donor by telephone to conduct a private medical interview. The purpose is to give the donor the opportunity to present any legitimate medical explanation for the laboratory finding, most commonly a valid prescription for a detected substance. If the donor provides documentation that the MRO can verify with the prescribing physician, the result may be reported to the employer as negative under 49 CFR Part 40.137.
If no legitimate explanation exists or documentation cannot be verified, the MRO reports a verified positive to the DER.
DER touchpoint: If the MRO cannot reach the donor after repeated contact attempts, the MRO contacts the employer’s Designated Employer Representative (DER) to facilitate contact. The DER should maintain current employee contact information and be directly reachable by the MRO team when a result requires action. Once the DER is notified, they have a defined window to arrange contact before the MRO may proceed to verify the result without a donor interview.
Employers who act on unreviewed non-negative laboratory results without proper MRO review increase exposure to wrongful termination claims, compliance disputes, and inconsistent testing program administration. Independent MRO review helps ensure that verified results are legally defensible and procedurally compliant before any employment action is taken.
The confidentiality protection built into this process means the employer receives only the verified result and the drug identified, not the donor’s medical history or the details of any prescription provided during the interview.
Role 3: Result Reporting and Confidentiality
Once the MRO has completed the review process and issued a verified result, that result is reported directly to the employer’s DER. Under 49 CFR Part 40.163, the MRO reports to the DER only, not to the employee, not to the collection site, and not to any other party unless specifically authorized.
Result categories the MRO may report include:
- Negative — no prohibited substance detected above cutoff levels, or a legitimate medical explanation was verified
- Positive — confirmed presence of a prohibited substance with no legitimate medical explanation
- Dilute Negative — specimen creatinine and specific gravity below normal ranges, requires specific employer handling
- Dilute Positive — specimen creatinine and specific gravity below normal ranges, confirmed presence of a prohibited substance with no legitimate medical explanation
- Substituted — specimen creatinine and specific gravity are inconsistent with normal human urine
- Adulterated — specimen contains a substance not expected in human urine
- Invalid — result cannot be reported due to an unresolvable specimen issue
- Canceled — test cannot be reported due to a fatal flaw or uncorrected error
- Refusal to test — donor did not complete the process, treated equivalently to a positive result under 49 CFR Part 40.305
For employers running DOT programs, the confidentiality requirements extend to how results are stored, who within the organization has access, and under what circumstances they may be shared. These requirements apply regardless of whether the employer manages their program internally or through a C/TPA.
What the MRO Must Know Under 49 CFR Part 40
The MRO must be thoroughly familiar with 49 CFR Part 40, with particular attention to the following subparts:
- Subpart G — Medical Review Officer and the Verification Process
- Subpart H — Split Specimen Tests
- Subpart I — Problems in Drug Tests
- Subpart P — Confidentiality and Release of Information
- Subpart Q — Roles and Responsibilities of Service Agents
- Subpart R — Public Interest Exclusions
- Appendix D — Report Format: Split Specimen Failure to Reconfirm
For additional MRO professional resources, the American Association of Medical Review Officers (AAMRO) provides certification, training, and ongoing guidance for practicing MROs.
MRO Review at PROCOM
PROCOM provides in-house MRO services for both DOT and non-DOT drug testing programs. Having an MRO on staff rather than routing results through a third-party MRO service means faster turnaround, a single point of contact from collection through verified result, and direct access to qualified medical review when questions arise.
PROCOM targets next-business-day reporting for verified negative results, with over 80% of tests meeting that timeline. Positive and non-negative results require additional MRO review steps, including the donor interview process, which can extend turnaround time depending on how quickly the donor responds and whether prescription documentation must be verified.
For non-DOT employers, MRO review is not federally required but is strongly recommended. Without it, employers acting directly on raw laboratory results carry legal exposure if a result had a legitimate medical explanation that was never evaluated. PROCOM’s MRO services are available for non-DOT programs under the same account structure as DOT testing.
Contact PROCOM to establish a company testing account or discuss MRO service requirements for your program.
Need Help Managing MRO Review?
PROCOM provides:
✔ In-house MRO services
✔ DOT & non-DOT review
✔ Faster verified results
✔ DER support and compliance guidance
Whether you are setting up a new testing program or improving an existing one, PROCOM can help simplify compliance and speed up result management.
Start your company testing program today.
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📧 michelle@procomtesting.com
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Regulatory Disclaimer: This content is provided for general informational and educational purposes regarding DOT and workplace drug and alcohol testing requirements. It does not constitute legal advice, official DOT regulatory interpretation, or company-specific compliance guidance. This content references regulations current as of [date]. Always verify you are applying current regulations and consult qualified legal counsel for definitive compliance requirements. PROCOM Testing provides DOT and non-DOT drug and alcohol testing services in accordance with 49 CFR Part 40. Compliance with drug and alcohol testing regulations is the employer’s responsibility.
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Compliance Resources: 49 CFR Part 40 | FMCSA Drug and Alcohol Rules | Supervisor Training | DOT Agency Requirements
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