An MRO-reviewed drug test is a test whose lab result goes to a Medical Review Officer before it reaches your employer. The MRO is a licensed physician who checks whether a non-negative result has a legitimate medical explanation, such as a valid prescription. Negative results move on quickly. Positive, adulterated, substituted, rejected and invalid results stop at the MRO’s desk first.

This guide explains what the MRO does, what the review looks like from the donor’s side and the employer’s side, how long it takes, and where people most often go wrong.

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TL;DR

  • An MRO is a licensed physician who reviews lab results and decides whether a non-negative result has a legitimate medical explanation. See the U.S. Department of Transportation’s MRO page.
  • A lab-positive result is not the final answer. The MRO verifies it, and only the verified result goes to the employer.
  • If the MRO’s office calls you, return the call quickly. Under DOT rules, the MRO may verify a test without hearing from you if you do not make contact within 72 hours of being told to.
  • The MRO is an independent reviewer, not your employer’s agent and not your treating doctor.
  • Employers get cleaner records and fewer disputes when every test in the program, DOT or not, runs through the same MRO process.

Table of Contents

What “MRO reviewed” actually means

The federal definition is short. An MRO is a licensed physician responsible for receiving and reviewing laboratory results generated by an employer’s drug testing program, and evaluating medical explanations for certain results. In practice, the MRO sits between two parties who both need a trustworthy answer: the laboratory, which measures what is in a specimen, and the employer, which needs to know whether a person can safely do a job.

A lab can tell you a specimen contained a substance or a metabolite. It cannot tell you why. The cause might be illicit use. It might also be a prescription, a medication taken as directed, or a specimen problem. The MRO’s job is to close that gap.

How lab findings move through MRO review

Under DOT rules, the MRO acts as an independent and impartial “gatekeeper” and an advocate for the accuracy and integrity of the testing process. That is not the same as being on the donor’s side or on the employer’s side.

What the MRO reviews

The MRO reviews results that are not simply negative:

  • confirmed positive results
  • adulterated specimens
  • substituted specimens
  • invalid results
  • rejected specimens

For DOT testing, the FMCSA’s implementation guidance says that all controlled substances testing laboratory results must be reviewed by a qualified MRO to verify and validate them. Many non-DOT employers adopt the same process voluntarily, because it protects both sides if a result is challenged.

What the MRO is not

Two misunderstandings come up constantly.

The MRO is not your employer’s agent. The MRO reports the final verified result to the employer’s designated representative, but federal rules limit what medical detail goes with it. The employer learns the outcome, not your full medical history, unless safety or the law requires more. See the rule on MRO responsibilities.

The MRO is not your doctor. The verification interview is not treatment or medical advice, and DOT describes it as not creating a doctor-patient relationship. The MRO is analyzing a lab result against your medical history and legitimate prescriptions.

How the process runs, step by step

  1. Collection. You provide a specimen at a collection site and complete the Custody and Control Form (CCF). The phone numbers you write on it matter later.
  2. Laboratory testing. The lab screens and, if needed, confirms the specimen.
  3. Negative results. These are reported on without any interview.
  4. Non-negative results. The lab sends them to the MRO, who must review them before anything goes to the employer.
  5. Contact attempts. The MRO or staff try to reach you. DOT’s rule calls for reasonable efforts, including at least three attempts over 24 hours using the numbers on the CCF.
  6. Verification interview. The MRO tells you the lab found a positive, adulterated, substituted or invalid result and asks about it. The opening of the interview is also set out in DOT’s rules.
  7. Decision. The MRO verifies the result as negative, positive, or another status such as a refusal to test, or cancels it.
  8. Report. The verified result goes to the employer’s designated representative.

If the MRO cannot reach you

If the MRO cannot reach you directly, the MRO contacts the Designated Employer Representative (DER), who is told to get you to call. After that, the clock is short. DOT’s rule says the MRO may verify the test without an interview if you decline, fail to make contact within 72 hours of the DER’s instruction, or stay unreachable for 10 days after the MRO receives the lab results.

Practical takeaway: if your HR contact says the MRO is trying to reach you, call back the same day. Silence is the one option that costs you the most.

Staff can call to schedule the interview but should not be asking about your medical details. If someone other than the MRO presses you for prescription information before the interview, treat that as a reason to pause and ask who they are.

If the MRO cannot reach you — overview diagram

What happens in the interview

The interview is the donor’s chance to give a medical explanation. Federal guidance describes a lab-confirmed positive as not automatically equal to drug misuse, and the interview as the employee’s opportunity to bridge the gap between the lab finding and their medical history.

Bring or be ready to describe:

  • every prescription and over-the-counter medication you take, with names, doses and dates
  • the prescriber’s name and contact details
  • any other medical circumstance you believe is relevant

The MRO may ask for pharmacy records or contact your prescriber. That is normal. Be accurate. An explanation the MRO cannot verify does not change the outcome, and an inaccurate one can make things worse.

Prescriptions and safety-sensitive jobs

A valid prescription can explain a positive. It does not always end the matter for a safety-sensitive role. If a medication could pose a safety risk, the MRO may ask you to have your prescriber consider whether another medication is appropriate. DOT’s rules set a short window for this, which is why the MRO’s instructions should be followed to the letter. Read the details in the MRO verification interview rule, and talk to your prescribing physician, not your employer, about any medication change. Never stop or switch a prescribed medicine on your own.

If you want a clinician’s perspective on how urine screens are used and verified in a medical practice, this clinician guide to telehealth urine drug screening describes the process from the treating side. It is a different setting from an employer program, so use it for background only.

How long does an MRO review take?

There is no single number. The rules do not set a maximum for the whole review, though the MRO must work in a timely way. What decides the pace:

Situation What to expect
Negative result Reported without an interview, usually quickly
Non-negative, donor answers promptly Interview can happen within a day or so of the MRO’s call
Donor hard to reach Three attempts over 24 hours, then the DER is involved
Donor never responds DOT allows verification after 72 hours from the DER’s instruction, or 10 days after the MRO gets the lab result
Prescription needs checking Extra time for pharmacy or prescriber confirmation

For employers, speed at the front of the process matters most. A fast, correct collection with a legible CCF and accurate phone numbers prevents most delays. When we perform collections, our typical turnaround to MRO-reviewed results is within 24 hours for results that need no further review.

Do MROs only call when you fail?

No, but practically yes, from the donor’s side. If your result is negative, there is normally no interview. The call comes when the lab reports a non-negative result. An MRO call is not a verdict. It is the step designed to prevent a person being labeled a drug user because of a lawful prescription or a lab or specimen issue.

A call about an invalid result is also not an accusation. It may mean the specimen could not be tested properly, and the MRO then decides whether a medical reason exists and whether a recollection is needed.

For employers: why MRO review protects you

If you run HR for a staffing agency, a trucking company, a construction firm or a healthcare employer, MRO review is the part of the program that most often decides whether it holds up when challenged.

  • Accuracy before action. You act on a verified result, not a raw lab finding.
  • Fewer disputes. A documented interview with a physician answers the usual “it was my medication” objection.
  • Clean paper trail. Auditors want to see CCFs, lab results, MRO verification and timelines. For DOT programs the rules in 49 CFR Part 40 are the benchmark.
  • Separation of roles. Because MROs are mandated to be impartial, including no financial interest in the labs they work with, your decisions rest on an independent review.

A few practical habits help:

  1. Keep your DER’s contact details current, so the MRO can reach the right person.
  2. Make sure donors write working phone numbers on the CCF.
  3. Do not act on a positive until the MRO has verified it.
  4. Do not ask donors what medications they take. That conversation belongs with the MRO.
  5. Store results and verification records where you can produce them on request.

For related compliance steps, see our guides on 24-hour MRO results for fit-for-duty testing, the DOT pre-employment test checklist, and what a non-negative result means and the next steps.

Our perspective: speed and paperwork are one problem

We see the same pattern in most delays. The lab is rarely the bottleneck. The bottleneck is a collection that was done late, a CCF with a wrong phone number, or an employer who could not be reached to tell a donor to call the MRO. A 15-minute walk-in collection and a clean form do more to shorten the MRO process than anything that happens later.

So we run collections the way an auditor would want to read them. Walk-in and same-day appointments cut the wait between a job offer and a completed test. Results are reviewed by an MRO, typically within 24 hours. The paperwork is written to stand up under DOT, OSHA and USCIS expectations. Employers get a record, and donors get a fair review.

Our advice to donors is simple: tell the collector about nothing you should not, but keep your medication list handy, give the correct phone number, and answer the MRO’s call. Our advice to employers is just as simple: let the MRO do the MRO’s job, and act only on the verified result.

— Total Tox

Testing with an MRO-reviewed result in the Bronx

If you need collections with MRO review, we serve employers and individuals from our Bronx clinic, with clients across the Bronx, Manhattan, Westchester and Queens. Our services include urine, saliva and hair testing, DOT drug and alcohol testing, DOT and employee physicals, immigration physicals, and fingerprinting. The clinic is bilingual and ADA-accessible, and you can walk in without waiting for a booking slot. If you are choosing between sample types, our hair follicle versus urine comparison lays out the differences. For more on DOT programs, browse our blog.

Common mistakes that slow or complicate a review

Wrong or unreachable phone numbers on the CCF. The MRO uses these numbers. If they fail, the process shifts to your employer and the 72-hour clock starts.

Ignoring a call from an unknown number. MRO offices often call from numbers you do not recognize. Check voicemail.

Sharing medication details with the wrong person. Supervisors and HR do not need your prescription list. The MRO does.

Assuming a prescription settles everything. For safety-sensitive work, the MRO may still need to consider the risk.

Employers acting too early. Removing someone from duty or sending a notice before verification can create avoidable legal exposure. Where a DOT employer must act after a verified positive, the next steps are in our guides to return-to-duty and follow-up testing.

A note on federal workplace programs

Not every MRO guide applies to every program. The 2024 SAMHSA guidance for federal workplace programs is its own document, and it states that it does not apply to specimens collected and tested under the DOT program. If you run a DOT-regulated operation, follow Part 40. If you run a federal agency testing program or a private policy, confirm which rules your program is under.

FAQ

What is an MRO in drug testing?

An MRO, or Medical Review Officer, is a licensed physician who receives laboratory drug test results and evaluates whether a non-negative result has a legitimate medical explanation. The MRO is independent of both the lab and the employer. Only the verified result is reported to the employer.

How long does it take for an MRO to review a drug test?

It depends on the result and on how quickly the donor responds. Negative results are reported without an interview. For non-negatives, the MRO makes at least three contact attempts over 24 hours, and DOT rules allow verification without an interview after 72 hours from the employer’s instruction or 10 days after the MRO receives the lab result. Prescription checks add time.

Do MROs only call if you fail?

They call when the lab reports a positive, adulterated, substituted, rejected or invalid result. A negative result normally brings no call. The call is not a final decision, and the interview is your chance to give a medical explanation.

Can the MRO tell my employer about my medications?

Not in general. The MRO reports the verified result to the designated employer representative and is limited in sharing medical details, unless they affect safe performance of safety-sensitive duties or the law requires disclosure. See 49 CFR 40.123.

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