Expanding Health Information Exchange Improves Identification of Frequent Emergency Department Users

Study objective: Frequent emergency department (ED) users are of interest to policymakers and hospitals. The objective of this study is to examine the effect of health information exchange size on the identification of frequent ED users. Methods: We retrospectively analyzed data from Healthix, a health information exchange in New York that previously included 10 hospitals and then grew to 31 hospitals. We divided patients into 3 cohorts: high-frequency ED users with 4 or more visits in any 30-day period, medium-frequency ED users with 4 or more visits in any year, and infrequent ED users with fewer than 4 visits in any year. For both the smaller (10-hospital) and larger (31-hospital) health information exchanges, we compared the identification rate of frequent ED users that was based on hospital-specific data with the corresponding rates that were based on health information exchange data. Results: The smaller health information exchange (n = 1,696,279 unique ED patients) identified 11.4% more high-frequency users (33,467 versus 30,057) and 9.5% more medium-frequency users (109,497 versus 100,014) than the hospital-specific data. The larger health information exchange (n = 3,684,999) identified 19.6% more high-frequency patients (52,727 versus 44,079) and 18.2% more medium-frequency patients (222,574 versus 192,541) than the hospital-specific data. Expanding from the smaller health information exchange to the larger one, we found an absolute increase of 8.2% and 8.7% identified high-and medium-frequency users, respectively. Conclusion: Increasing health information exchange size more accurately reflects how patients access EDs and ultimately improves not only the total number of identified frequent ED users but also their identification rate.