March 2021. Only 37% of office-based physicians are able to send data electronically to outside providers to whom they refer patients. Within this group, little is known about the factors related to varying levels of use of these technologies. We investigated variation in the percentage of referrals that office-based providers sent with electronic care summary data. Providers with exchange capabilities only used these tools in about half of referrals, leaving millions of transitions of care without accompanying information for the consulting provider to review.