Missed opportunity: patients who leave emergency departments without being seen.

The rate of patients who visit emergency departments (EDs) but leave before being evaluated and treated is an important indicator of ED performance. This study examines patient- and hospital-level characteristics that may increase the risk of patients leaving EDs before being seen. The data are from the National Ambulatory Care Reporting System, an administrative database, and represent 4.3 million patient visits made to 163 Ontario EDs between April 2003 and March 2004. Among these data, the proportion that left without being seen (LWBS) was 3.1% (136,805). The rate of LWBS was highest among patients aged 15 to 35 years, those with less acute conditions and facilities that handle the highest volume of patients. Facility rates were positively correlated with facility median ED length of stay, annual facility volume and percentage of inpatient admissions. Understanding patient and facility characteristics that increase rates of LWBS may inform the process of developing measures to ensure timely access to ED care for all who seek it.