The Court of Special Appeals overturned the trial court's ruling as to the medical negligence claim. It held that Dr. Debrun did not dedicate more than 20% of his professional activities to activities directly involving testimony, and he was therefore qualified to testify as to the standard of care pursuant to the rule. The Court of Appeals granted certiorari to determine whether the Court of Special Appeals properly interpreted the 20% rule. The Court of Appeals reversed the judgment of the Court of Special Appeals.

UMMS and Dr. Zoarski argued to the Court of Appeals that Dr. Debrun's activities – conducting peer review, reading journals, observing procedures, discussing patients with former colleagues, and attending conferences – were not "professional activities" in the sense of relating to the profession of medicine. According to them, Dr. Debrun was retired, all of his professional activities were for the purpose of testifying in medical malpractice cases; and therefore 100 percent of his time was dedicated to activities directly related to giving testimony. Allowing him to qualify as an expert witness, they contended, eliminated the purpose of the requirement, allowing professional witnesses to criticize practicing doctors without themselves being members of the profession. The Waldt's countered by reasoning that Dr. Debrun's activities were "professional activities," but did not directly relate to giving testimony in medical malpractice cases.

MD. CODE ANN., CTS. JUD. PROC. ¶ 3-2A-04(b)(4) states that an expert "may not devote annually more than twenty percent of the expert's professional activities to activities that directly involve testimony in personal injury claims." Therefore, to discern whether an expert is qualified to testify under this requirement, the courts must perform a mathematical equation: judges must identify those activities that "directly involve testimony in personal injury claims" (the numerator) and then divide by those activities that comprise the body of "professional activities" in general (the denominator). The center of activities that counts as the numerator (i.e. activities that "directly involved testimony") include: (1) the time the doctor spends traveling for testimony purposes; (2) the time spent assisting an attorney in responding to discovery; (3) the time spent in reviewing materials, preparing reports, and conferring with attorneys when the doctor is aware that he will likely be called upon to sign an affidavit or otherwise testify; and (4) the time spent on any similar activity that has a clear and direct relationship to testimony to be given by the doctor or the doctor's preparation to give testimony.

The Court of Appeals, however, had yet to rule on the meaning of the phrase "professional activities" as is it used in the 20% rule. The Court of Appeals concluded that activities are "professional activities" when the activity contributes to or advances the profession to which the individual belongs or involves the individual's active participation in that profession. Professional activities include time devoted to testifying and engaging in peer review of journal articles, but do not include time devoted to reading journal articles, observing procedures, discussing patients with outer professionals, and attending conferences when those activities are undertaken for personal reasons.

Under the Court of Appeals' construction of professional activities, however, Dr. Debrun's professional activities were limited to testifying in medical malpractice cases and assisting with peer review of medical journals. His work involving peer review of medical journals qualified as "professional," even though he was not paid for his time, because he was contributing to the profession. He was utilizing his knowledge gained through years of experience and was advancing his field. Dr. Debrun's other activities, however, despite being related to the field of interventional neuroradiology, did not actively contribute to the development or advancement of the field or involve his active participation in the field and were therefore not professional activities. Such activities included reading journals for pleasure, observing medical procedures for his own personal knowledge, discussing patients with former colleagues, and attending conferences.

Under this classification, Dr. Debrun devoted 50 hours annually to activities directly involving testimony and 242 hours total to professional activities annually (50 hours on testimony and 192 hours on peer review). Therefore, Dr. Debrun devoted 20.66% of his professional time to activities directly involving testimony and did not satisfy the 20% rule and was properly excluded from testifying regarding the standard of care.