A Laboratory Result Is Not Always the Employer’s Final Result
When an employer receives workplace drug-testing services, the laboratory is only one part of the process. For DOT-regulated testing, a laboratory-confirmed positive, adulterated, substituted, or invalid result normally goes to a Medical Review Officer before a final verified result is reported to the employer. A medical review officer drug test process provides an independent medical review between laboratory analysis and the employment-related result delivered to the company. Under current 49 CFR Part 40, the MRO reviews required documentation, conducts a verification interview when applicable, considers legitimate medical explanations, and determines the final verified result.
This distinction matters for employers managing safety-sensitive positions, transportation operations, construction projects, and industrial workforces. Gulf Coast Occupational Medicine provides employer-focused occupational health services that currently include drug and alcohol testing, laboratory services, clinic-based care, and mobile testing capabilities. Its current drug-testing resources also discuss coordination among collections, laboratories, MROs, and employer reporting.
The DOT procedures discussed below apply specifically to testing governed by 49 CFR Part 40. Non-DOT testing can follow different employer policies, state laws, contracts, or program requirements, so employers should not automatically apply DOT procedures to every workplace drug test.
What Does a Medical Review Officer Do?
For DOT testing, an MRO must be a licensed physician who meets specific training, examination, and continuing qualification requirements. The MRO serves as an independent medical reviewer rather than simply passing a laboratory result to the employer.
The MRO drug testing process includes reviewing the Custody and Control Form, checking for errors that could affect the test, reviewing laboratory documentation, contacting the employee when required, assessing medical information, and determining whether the result should ultimately be verified as negative, positive, canceled, or a refusal because of adulteration or substitution.
This is why a non-negative drug test result should not automatically be treated as a verified positive.
Drug Testing Process Diagram
Specimen Collection and Chain of Custody
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Laboratory Testing
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Laboratory Reports Result to MRO
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MRO Reviews CCF and Laboratory Documentation
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Confidential MRO Verification Interview, When Required
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Prescription or Other Legitimate Medical Explanation Reviewed
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MRO Makes Final Verification Decision
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Final Result Reported to the Designated Employer Representative
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If Applicable, Employee Is Informed of Split-Specimen Rights
What Happens During the MRO Verification Interview?
When the MRO receives a laboratory-confirmed positive, adulterated, substituted, or invalid result, the MRO generally must contact the employee directly and confidentially. The employee is given an opportunity to discuss the result before the MRO makes the verification decision.
During the MRO verification interview, the physician reviews relevant medical history and other biomedical information supplied by the employee. If the employee states that a prescription medication explains a laboratory-confirmed result, the MRO must take reasonable steps to authenticate the supporting medical information. This can include verifying prescription records with the prescribing professional or pharmacy.
This positive drug test prescription review is one reason laboratory confirmation and MRO verification are separate steps.
For certain DOT-tested drugs, if the employee establishes a legitimate medical explanation, such as an appropriately verified legally valid prescription, the MRO can verify the result as negative rather than positive. If no legitimate explanation is established, the MRO verifies the laboratory-confirmed result as positive.
Employers should not ask supervisors or HR personnel to independently decide whether an employee’s prescription explains a test result. That medical review belongs within the appropriate MRO process.
What Should Employers Do While MRO Review Is Pending?
A common mistake is treating a laboratory-confirmed result as though the employer has already received a final positive.
For DOT-regulated testing, employers generally cannot stand an employee down based solely on the MRO’s receipt of a laboratory-confirmed positive, adulterated, or substituted result unless the employer has a specific DOT agency waiver permitting a compliant stand-down program. Without that waiver, the MRO generally cannot disclose the pending laboratory result before completing verification.
Employers should instead:
- Keep their designated employer representative contact information current.
- Allow the MRO to complete the confidential medical review.
- Avoid asking employees to provide prescription details directly to ordinary supervisors.
- Wait for the verified result before applying DOT consequences unless an applicable rule specifically provides otherwise.
- Maintain separate procedures for DOT and non-DOT programs.
- Document communications and actions required by the applicable testing program.
Once a DOT employer receives a verified positive result, the applicable employer responsibilities begin, including immediate removal from DOT safety-sensitive functions.
If your organization needs to coordinate clinic-based or on-site workplace testing, Gulf Coast Occupational Medicine’s occupational health services currently include drug and alcohol testing and laboratory capabilities. Employers can also review GCOM’s guidance on digital and on-site drug testing when planning workforce testing workflows.
What Happens With Adulterated or Substituted Results?
An adulterated or substituted laboratory result also requires MRO review. Under DOT rules, the MRO generally follows a verification process similar to a confirmed positive result and gives the employee an opportunity to provide a legitimate medical explanation for the laboratory findings. If no acceptable explanation is established, an adulterated or substituted result is verified as a refusal to test.
Employers should therefore avoid assuming that every unusual laboratory finding has the same meaning. The MRO determines the appropriate verified result under Part 40.
What if the MRO Cannot Reach the Employee?
The regulations establish a documented contact process.
The MRO or MRO staff must make reasonable attempts to contact the employee, including at least three attempts reasonably spaced over a 24-hour period. If direct contact cannot be made, the MRO contacts the designated employer representative, who attempts to reach the employee while protecting confidentiality and instructs the employee to contact the MRO.
In specified circumstances, the MRO can eventually verify a positive or refusal without an interview. This can occur if the employee declines the interview, fails to contact the MRO within 72 hours after documented DER contact, or cannot be reached despite documented reasonable efforts within 10 days after the MRO received the laboratory-confirmed result.
Split-Specimen Requests Provide an Additional Safeguard
After a verified positive result or a refusal based on adulteration or substitution, the MRO must tell the employee about the right to request testing of the split specimen.
For DOT testing, the employee generally has 72 hours after receiving notice from the MRO to request split-specimen testing. The employer must ensure the test occurs when a timely request is made, although the employer may seek reimbursement from the employee as permitted by the regulation.
A split-specimen request does not mean the employer waits to act on a verified positive DOT result. Once the employer receives the verified result, Part 40 requires the applicable safety-sensitive removal even while split-specimen testing is pending.
Confidentiality and Final Reporting to the Employer
The MRO reports DOT drug-test results to the designated employer representative, either directly or through an authorized consortium/third-party administrator when allowed. The reported result may include categories such as negative, positive, canceled, or refusal to test and, for verified positives, the applicable drug or metabolite.
That does not mean the employer automatically receives every detail discussed during the employee’s medical interview. DOT rules require MROs to protect drug-testing confidentiality, although certain medical information affecting safe performance may have to be communicated under specific circumstances.
The practical lesson is simple: keep medical verification separate from ordinary HR speculation. Employers need the verified result and information they are legally entitled to receive, not unrestricted access to an employee’s medical history.
Hypothetical Example: A Baton Rouge Contractor Mobilizing Workers
Hypothetical scenario: A Baton Rouge industrial contractor is preparing 75 employees for a major project. Some employees perform DOT-regulated transportation duties, while others are covered by the company’s non-DOT program.
One DOT specimen produces a laboratory-confirmed result requiring MRO review. The employer’s DER does not independently question the employee about prescriptions or treat the laboratory finding as a final verified positive. Instead, the MRO contacts the employee and conducts the required review.
The employee provides prescription documentation. The MRO authenticates the information and determines whether it constitutes a legitimate medical explanation under the applicable DOT rule. Only after the verification process is completed does the employer receive the final result.
This example shows why employers should clearly identify DOT versus non-DOT testing before collection and maintain reliable communication among the collection site, laboratory, MRO, and DER.
For employers handling large workforces, GCOM’s current construction drug-testing resources emphasize planning for laboratory and MRO coordination alongside collection and confidential employer reporting.
Build a Drug-Testing Process Around Verified Results
A well-organized medical review officer drug test process protects the integrity of workplace testing by separating laboratory findings from final medical verification. Employers should understand the role of the MRO, maintain accurate DER information, protect employee confidentiality, distinguish DOT from non-DOT testing, and avoid acting on preliminary information as though it were a verified result.
Gulf Coast Occupational Medicine provides workplace drug and alcohol testing, laboratory services, occupational health screenings, and mobile/on-site services for employers across Louisiana and beyond. Because the website describes coordination with laboratories and MROs rather than identifying Gulf Coast itself as the MRO for every program, employers should confirm the specific MRO arrangement for their testing program when scheduling services.
Call Gulf Coast Occupational Medicine at (225) 753-7233 to discuss workplace drug and alcohol testing services and the testing workflow appropriate for your workforce. The current main phone number is confirmed on GCOM’s contact and locations pages.
Frequently Asked Questions
Is a laboratory non-negative result automatically a positive drug test?
No. In DOT testing, a laboratory-confirmed positive, adulterated, substituted, or invalid result normally goes through MRO review before the MRO reports the final verified result to the employer.
Can a prescription change a positive drug test result?
For certain DOT-tested drugs, yes. During the positive drug test prescription review, the employee may provide evidence of a legitimate medical explanation. The MRO verifies prescription information and determines whether the result should be reported as negative or positive under the applicable rules.
How long does an employee have to request split-specimen testing?
For a DOT verified positive or a refusal based on adulteration or substitution, the employee generally has 72 hours from MRO notification to request testing of the split specimen.
What happens if an employee does not return the MRO’s call?
The MRO and DER must follow specific documented contact procedures. Depending on what contacts occur and how much time passes, DOT rules can permit the MRO to complete verification without an employee interview.
