Every DOT drug test result passes through the same set of hands before it becomes official: the Medical Review Officer. The Medical Review Officer is one of the least understood roles in the DOT drug testing process, yet their decision determines whether a test result is verified positive or negative. Here’s what employers and drivers need to know about what the Medical Review Officer does and why it matters.
What Is a Medical Review Officer (MRO)?
A Medical Review Officer (MRO) is a licensed physician — either an MD or DO — who has received specialized training in DOT federal workplace drug testing regulations and the medical review of DOT-regulated drug test results. Under 49 CFR Part 40 Subpart G, every DOT-regulated drug test result from a SAMHSA-certified laboratory must be reviewed and verified by a qualified MRO before the employer receives the result.
The MRO serves as an independent clinical safeguard in the testing process. Their job is to receive the laboratory’s findings, evaluate whether the result is scientifically valid, determine whether there is a legitimate medical explanation for a positive or unusual result, and issue the final verified result to the employer. The MRO is not an advocate for the driver or the employer — they are a neutral clinical reviewer whose decisions are based on regulated medical criteria.
Without an MRO in the chain of custody, a positive result from the laboratory is not a DOT-verified positive. The employer cannot take adverse action — including removal from safety-sensitive duties — based solely on a laboratory report. The verified result from the MRO is the official DOT drug test result.
Medical Review Officer Qualifications and Training
Under 49 CFR 40.121, a Medical Review Officer must be a licensed physician (MD or DO) and must have completed qualification training in DOT federal workplace drug testing regulations. Qualification training covers: the DOT drug testing program and the role of the MRO, the basics of pharmacology for drugs covered by DOT testing, the medical basis for the review process, and the criteria for verifying positive, negative, cancelled, and refusal results.
In addition to initial qualification training, MROs must complete requalification training every five years to remain current on regulatory changes and updated testing protocols. MROs are also required to stay current on any ODAPC guidance documents that affect the review process. The DOT maintains a list of MRO training providers who offer accredited qualification and requalification courses.
Employers who work with a C/TPA or collection network typically use an MRO provided through those services rather than contracting directly with an MRO. Regardless of how the MRO is engaged, the employer is responsible for ensuring that any MRO reviewing their employees’ tests is properly qualified under 49 CFR 40.121.
How the Medical Review Officer Review Process Works
After a DOT drug test specimen is collected at a certified collection site and shipped to a SAMHSA-certified laboratory, the laboratory tests the specimen for the five panels of drugs covered by DOT testing: marijuana (THC), cocaine, amphetamines/methamphetamine, opioids (including heroin and fentanyl analogs), and phencyclidine (PCP). The laboratory reports its findings to the MRO — not directly to the employer.
When the MRO receives a laboratory result showing a positive, adulterated, substituted, or invalid finding, they begin the medical review process. First, they verify the chain-of-custody documentation — the Custody and Control Form (CCF) — to confirm the specimen was collected, handled, and tested according to federal requirements. If the chain of custody is intact, they proceed with the medical review.
For a positive result, the MRO contacts the donor (the driver) directly to conduct a verification interview. This interview is the driver’s opportunity to provide any legitimate medical explanation for the positive result — such as a valid prescription for a medication that triggered the positive finding. The MRO evaluates whether the explanation is medically valid and consistent with the laboratory finding.
When the Medical Review Officer Contacts the Driver
Under 49 CFR 40.131, when the MRO receives a laboratory-confirmed positive, adulterated, substituted, or invalid result, they must make a reasonable effort to contact the donor directly before verifying the result. The MRO must attempt to reach the driver at the phone number on the CCF and must make at least two contact attempts within a 24-hour period.
If the MRO cannot reach the driver directly, they contact the employer’s DER (Designated Employer Representative) and ask the DER to have the driver contact the MRO within 72 hours. The driver has 72 hours from the DER notification to contact the MRO with a legitimate medical explanation. If the driver does not contact the MRO within 72 hours and provides no explanation, the MRO verifies the result as positive.
Drivers should always answer calls from unknown numbers during and after the drug testing process, as the MRO contact is often the only opportunity to provide a medical explanation for a positive laboratory result. Once the 72-hour window closes without driver contact, the result is verified positive and the return-to-duty process begins.
Verified Positive, Negative, and Refusal Results
After conducting the medical review, the MRO issues one of the following verified results: negative (laboratory was positive but driver provided a legitimate medical explanation), positive (laboratory was positive and no legitimate medical explanation exists), cancelled (test cannot be used due to a procedural flaw), refusal to test (driver’s behavior during collection constituted a refusal under 49 CFR 40.191), or a negative with a safety concern notation in certain circumstances.
A verified negative result — even when the laboratory showed a positive — is treated exactly the same as any other negative result. The employer takes no adverse action and the result is not reported to the Clearinghouse as a violation. A verified positive result is reported to the Clearinghouse, triggers mandatory removal from safety-sensitive duties, and initiates the return-to-duty process.
A cancelled result means the test cannot be used but is not a positive. The employer must conduct an immediate recollection under direct observation for a cancelled pre-employment or random test. A “refusal to test” finding is treated identically to a positive — the driver is removed from duty, the violation is reported to the Clearinghouse, and the SAP/RTD process begins.
Split Specimen Requests
When a DOT drug test specimen is collected, the collection site fills two containers: the primary (Bottle A) and the split (Bottle B). Both containers are sealed and sent to the laboratory, but only Bottle A is tested initially. If the MRO verifies the primary specimen as positive, adulterated, or substituted, the driver has 72 hours from receiving notification to request that Bottle B be sent to a second SAMHSA-certified laboratory for retesting.
The request for split specimen testing must be made directly to the MRO within 72 hours. The MRO cannot grant an extension beyond 72 hours except in documented extraordinary circumstances. If the driver requests split specimen testing, the MRO puts the verification on hold until the Bottle B result is received. If Bottle B confirms the positive, the original verified result stands. If Bottle B does not confirm, the entire test is cancelled.
Employers should be aware that a pending split specimen request does not suspend the requirement to remove the driver from safety-sensitive duties. The driver remains off safety-sensitive duties until the MRO issues the final verified result, whether that is after the initial verification or after the Bottle B result returns.
How the Medical Review Officer Reports Results
The MRO reports verified results to the employer’s Designated Employer Representative (DER) — the person at the company who is designated to receive drug test results and manage the compliance response. The MRO may communicate results by phone, fax, or electronic record management system, depending on the systems in use by the employer or C/TPA.
For negative results, the MRO typically reports results within 24–72 hours of receiving the laboratory report. For positive, adulterated, or substituted results that require a donor interview, the timeline is longer — typically 3–5 business days after the laboratory report, depending on how quickly the MRO can complete the verification interview and how responsive the driver is.
MROs are prohibited from releasing verified results to anyone other than the employer’s DER or the employer’s C/TPA. They cannot release results to the driver directly (though the driver may request a copy of their results from the MRO after the verification is complete), and they cannot release results to other employers without the driver’s written consent.
Frequently Asked Questions: Medical Review Officer
Can an employer choose their own MRO?
Employers may contract directly with a qualified MRO, or they may use an MRO provided through their C/TPA or collection network. Either approach is acceptable as long as the MRO is qualified under 49 CFR 40.121. Employers who use a C/TPA typically have an MRO assigned to them as part of the service package.
What happens if a driver misses the MRO’s call?
The MRO must make at least two attempts to reach the driver within 24 hours. If unsuccessful, they notify the employer’s DER, who then has the driver contact the MRO within 72 hours. If the driver fails to contact the MRO within that window without a valid explanation, the MRO verifies the result as positive. Drivers should always answer unknown calls during and after testing.
Can an MRO change a positive result to negative?
Yes. If the driver provides a legitimate medical explanation for the positive — such as a valid prescription for a medication that triggered the result, with documentation from the prescribing physician — and the MRO determines the explanation is clinically valid and consistent with the laboratory finding, the MRO may verify the result as negative. The employer takes no adverse action on a verified negative result.
How long does the MRO review process take?
Negative results are typically reported within 1–3 business days after the laboratory releases its report. Results requiring a donor interview (positive, adulterated, or substituted laboratory findings) typically take 3–7 business days, depending on how quickly the MRO can complete the verification interview and how responsive the driver is.
Does the driver have to talk to the MRO?
Yes. For any non-negative laboratory result, the MRO must attempt to contact the driver before verifying the result. While the driver technically cannot be forced to speak to the MRO, refusing to do so or failing to contact the MRO within 72 hours of the DER notification results in the positive being verified without any opportunity to provide a medical explanation. The driver has no further recourse after the 72-hour window closes.
Stay Compliant With Vertical Identity
A qualified MRO is a required component of any DOT-compliant drug testing program — not an optional add-on. Vertical Identity’s C/TPA services include access to certified MRO review for all drug tests in your program, ensuring that every result is verified by a qualified physician and reported accurately and on time.
Get started with Vertical Identity to access a fully compliant DOT drug testing program including MRO services, collection network access, and Clearinghouse management. Learn more about our DOT random testing program.