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Qual Saf Health Care. 2007 Apr;16(2):127-31.

Ambulatory care adverse events and preventable adverse events leading to a hospital admission.

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  • 1Institute for Healthcare Studies, Feinberg School of Medicine, Northwestern University, Chicago, Illinois 60611, USA.



Most healthcare in the US is delivered in the ambulatory care setting, but the epidemiology of errors and adverse events in ambulatory care is understudied.


Using the population-based data from the Colorado and Utah Medical Practices Study, we identified adverse events that occurred in an ambulatory care setting and led to hospital admission. Proportions with 95% CIs are reported.


We reviewed 14,700-hospital discharge records and found 587 adverse events of which 70 were ambulatory care adverse events (AAEs) and 31 were ambulatory care preventable adverse events (APAEs). When weighted to the general population, there were 2608 AAEs and 1296 (44.3%) APAEs in Colorado and Utah, USA, in 1992. APAEs occurred most commonly in physicians' offices (43.1%, range 46.8-27.8), the emergency department (32.3%, 46.1-18.5) and at home (13.1%, 23.1-3.1). APAEs in day surgery were less common (7.1%, 13.6-0.6) but caused the greatest harm to patients. The types of APAEs were broadly distributed among missed or delayed diagnoses (36%, 50.2-21.8), surgery (24.1%, 36.7-11.5), non-surgical procedures (14.6%, 25.0-4.2), medication (13.1%, 23.1-3.1) and therapeutic events (12.3%, 22.0-2.6). Overall, 10% of the APAEs resulted in serious permanent injury or death. The proportion of APAEs that resulted in death was 31.8% for general internal medicine, 22.5% for family practice and 16.7% for emergency medicine.


An estimated 75,000 hospitalisations per year are due to preventable adverse events that occur in outpatient settings in the US, resulting in 4839 serious permanent injuries and 2587 deaths.

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