About 49% of health referrals involved health information exchanges (HIEs) via electronic summaries of care (eSCR) during 2016, according to health care professional attestations for the federal Meaningful Use electronic health record (EHR) incentive program. Primary care professionals used HIE to make 43% of referrals, compared to 57% among professionals not in a primary care specialty. Practice-level factors were more commonly associated with greater levels of HIE use than market-level factors. The analysis considered the effects of nine practice-level factors. Four were related to practice structure and operations: EHR platform used, practice size, health system membership, and . . .