A Medical Review Officer (MRO) is a licensed physician, an MD or DO, who reviews lab results and evaluates medical explanations for certain drug test results. (source) If the MRO is calling you, the lab found something that needs a medical explanation before the result is final. Call back.
Student drug screens for clinicals aren't regulated by the Department of Transportation, but schools and reviewing doctors often follow the same federal procedures. Washington State University's policy, for example, cites the federal MRO guidance manual. The federal rules below show how the process usually works.
How the MRO reaches you
- The MRO must actually talk to you. Staff may schedule the call but can't collect medical information.
- "Reasonable efforts" means at least three attempts spread over 24 hours, to the numbers on your custody form. (source)
Deadlines
- Under the federal rule, the MRO can verify a result without talking to you if you decline, if 72 hours pass after you were told to call, or if nobody can reach you within 10 days. (source)
- Schools can be stricter. UW–Madison: when a student doesn't respond to MRO calls, "a positive drug screen is uploaded." (source) WSU treats a non-response within the MRO's timeframe as positive. (source)
Prescriptions
The MRO verifies a positive unless there's a legitimate medical explanation, like a valid prescription, and won't second-guess whether your doctor should have prescribed it. You carry the burden of proof. (source) Have the pharmacy label or your prescriber's information ready. See prescriptions and drug tests.
Medical marijuana cards and CBD are not accepted as explanations under the federal rules. See marijuana, CBD and clinical drug tests.
Sources
- 49 CFR Part 40, Subpart G (Medical Review Officers)
- UW–Madison SMPH: Positive drug screen, missed MRO calls
- WSU College of Nursing drug screening policy
General information from public federal documents and published school policies as of September 2026, not medical or legal advice. Your program and clinical sites set the rules that apply to you.
Frequently asked questions
Why is an MRO calling me?
The lab found a result that needs a medical explanation before it's final, for example a prescription. Call back as soon as you can.
What happens if I don't call the MRO back?
Under the federal rule, the result can be verified without you. Many schools treat a non-response as a positive; UW–Madison uploads a positive screen when a student doesn't respond.
What should I have ready?
Your prescription information: the pharmacy label or your prescriber's name and phone number.
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