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The Role of a Medical Review Officer (MRO) in Drug Testing

Employment drug testing loves its acronyms, and ‘MRO’ is among the most relevant to both employer and job candidate/employee.

A Medical Review Officer (MRO) is a licensed physician who acts as an advocate for the donor, working to ensure the integrity of the drug screening process.

The MRO is responsible for evaluating laboratory drug test results and communicating with the donor to determine possible medical explanations. That way, accurate results can be reported to the employer without disclosing personal medical information, such as valid prescriptions.

There can be legitimate explanations for confirmed positives, adulterated specimens, and invalid drug results. These are things that need to be uncovered before the employer is notified.

Duties of an MRO

Here are the primary responsibilities of a Medical Review Officer:

  • Review all positive results.
  • Review all lab-rejected specimens.
  • Review (at least) 5 percent of negative results to ensure lab testing accuracy.
  • Discuss invalid results with the lab and determine whether further testing is necessary
  • Maintain all records for at least two years.
  • Communicate directly with the donor to ensure the integrity of results; this may involve conducting a general medical evaluation.
  • Sometimes, the MRO may contact the employer if contact can’t be made with the donor.

At Peopletrail, every test that yields an initial positive result will be sent to the laboratory for further testing and will ultimately be reviewed by an MRO.

MRO review concept

Frequently Asked Questions


How does the MRO notify a candidate about non-negative drug test results?

When the MRO receives a confirmed positive, adulterated, substituted, or invalid test result from the laboratory, they initiate contact with the employee directly, on a confidential basis, to determine whether the candidate wants to discuss the test result. 

In making this contact, the MRO explains to the candidate that if they decline to discuss the result, the test will be reported as positive or as a refusal to test because of adulteration or substitution, as applicable.

Staff under the personal and close supervision of the MRO may conduct this initial contact on their behalf.

What are the standard “unable to contact” protocols?

The MRO will make reasonable attempts to reach the candidate at the day and evening telephone numbers listed on the chain of custody form. Reasonable efforts include a minimum of three attempts, spaced reasonably over a 24-hours. If the candidate cannot be reached despite these efforts, the following apply:

  • Contact efforts are documented in detail, including dates and times. If both phone numbers are incorrect (e.g., disconnected, wrong number), the MRO may contact the Designated Employer Representative (DER), instructing the DER to contact the employee.
  • The MRO may direct the DER to inform the employee to contact them.
  • The MRO must not inform the DER that the employee has a confirmed positive, adulterated, substituted, or invalid test result.
  • The MRO must document the dates and times of their attempts to contact the DER, as well as the name of the DER that was contacted.

How are THC-positive results handled?

Peopletrail’s MRO network is regulated by federal guidelines. As of the publication of this article, THC remains federally banned. Thus, if THC is included on the drug testing panel, its appearance in a result will prompt a standard MRO review process.

In most instances, however, employers reserve the choice to include or exclude THC from their drug testing panel.

How long does the MRO process take?

Ideally, the process takes no more than 24 hours. 

However, if the donor is difficult to reach, timeliness could be extended to 4 days or more. For this reason, we encourage our clients to brief their candidates and make them aware of possible MRO outreach. 

A 24-48 hour completion (after lab testing) is a reasonable expectation when things move smoothly.

Are false positives a possibility?

False positives are possible but very rare. 

While no testing method is infallible, most laboratories utilize both Immunoassay and GC-MS (Gas Chromatography Mass Spectrometry) methods on each sample tested. Thus, testing errors are very unlikely.

The more common cause of false positives is substance interference. Many substances that can affect results are common foods and over-the-counter medications. Here is a list of common substances and the associated drugs they can trigger a positive result for:

  • Ibuprofen: Barbituates or Benzodiazepines
  • Cold medicine: Amphetamines
  • Allergy medicine: Amphetamines
  • Nasal decongestants: Amphetamines
  • Diet pills: Amphetamines
  • Sleep aids: Barbituates
  • Poppy seeds: Opiates
  • Hemp food products: Marijuana

Note: Positives resulting from the use of common substances above are uncommon and can be clarified by MRO evaluation.


The MRO is a necessary gatekeeper between the drug testing lab and the employer. MRO expertise helps determine the true nature and reportable validity of a confirmed positive, adulterated, or invalid sample.

The medical review process is in place to help the donor and ensure that the drug testing results reported are fair and accurate.

For more information about Peopletrail drug testing services, visit us online.

Additional Reading

How Long Are Substances Detectable by a Drug Test?
Need-To-Know DOT Drug Screening Basics
Things to Consider When Establishing a Drug Testing Program
Answering Your Common Drug Test Questions


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