Importance: Current efforts to improve health care focus on hospital readmission rates as a marker of quality and on the effectiveness of transitions in care during the period after acute care is received. Emergency department (ED) visits are also a marker of hospital-based acute care following discharge but little is known about ED use during this period.

Objectives: To determine the degree to which ED visits and hospital readmissions contribute to overall use of acute care services within 30 days of discharge from acute care hospitals, to describe the reasons patients return for ED visits, and to describe these patterns among Medicare beneficiaries and those not covered by Medicare insurance.

Design, setting, and participants: Prospective study of patients aged 18 years or older (mean age: 53.4 years) who were discharged between July 1, 2008, and September 31, 2009, from acute care hospitals in 3 large, geographically diverse states (California, Florida, and Nebraska) with data recorded in the Healthcare Cost and Utilization Project state inpatient and ED databases.

Main outcome measures: The 3 primary outcomes during the 30-day period after hospital discharge were ED visits not resulting in admission (treat-and-release encounters), hospital readmissions from any source, and a combined measure of ED visits and hospital readmissions termed hospital-based acute care.

Results: The final cohort included 5,032,254 index hospitalizations among 4,028,555 unique patients. In the 30 days following discharge, 17.9% (95% CI, 17.9%-18.0%) of hospitalizations resulted in at least 1 acute care encounter. Of these 1,233,402 postdischarge acute care encounters, ED visits comprised 39.8% (95% CI, 39.7%-39.9%). For every 1000 discharges, there were 97.5 (95% CI, 97.2-97.8) ED treat-and-release visits and 147.6 (95% CI, 147.3-147.9) hospital readmissions in the 30 days following discharge. The number of ED treat-and-release visits ranged from a low of 22.4 (95% CI, 4.6-65.4) encounters per 1000 discharges for breast malignancy to a high of 282.5 (95% CI, 209.7-372.4) encounters per 1000 discharges for uncomplicated benign prostatic hypertrophy. Among the highest volume discharges, the most common reason patients returned to the ED was always related to their index hospitalization.

Conclusions and relevance: After discharge from acute care hospitals in 3 states, ED visits within 30 days were common among adults and accounted for 39.8% of postdischarge hospital-based acute care visits. Improving care transitions should focus not only on decreasing readmissions but also on ED visits.