MRO Review Medical Review Officer An essential part of the drug- testing program is the final review of negative and positive results from the laboratory. A positive test result does not automatically identify an employee/ applicant as having used drugs in a violation of DOT agency regulations. An individual with a detailed knowledge of possible alternate medical explanations is essential to the review of results. This review shall be performed by the Medical Review Officer (MRO) prior to the transmission of the results to the employer administrative officials.