Medical errors and other adverse events occur in one-third of hospital admissions–as much as 10 times more than some previous estimates have indicated, according to a new study.

Health Affairs, a peer-reviewed journal focusing on health policy, published this finding in its April edition. The publication is an arm of Project HOPE, a nonprofit international health education organization.

The patient safety study, conducted by David Classen of the University of Utah and coauthors at the Institute for Healthcare Improvement, compared three methods for detecting adverse events in hospitalized patients, including the Institute’s own Global Trigger Tool. The study drew on comparable samples of patients from three leading hospitals that had undertaken quality and safety improvement efforts.

Among the 795 patient records reviewed, voluntary reporting detected four “events,” the Agency for Healthcare Research and Quality (AHRQ) Indicators detected 35, and the Global Trigger Tool detected 354 events, ten times more than the AHRQ method.

The AHRQ indicators and voluntary reporting thus missed more than 90% of adverse events identified by the Global Trigger Tool, the study authors says. The authors add their findings are “conservative” because they rely on medical record review, which would not detect as many adverse events as direct, real-time observation would.

The researchers say that reliance on voluntary hospital reporting or the AHRQ indicators could lead to seriously flawed perceptions of patient safety in the U.S. They also note that the Global Trigger Tool detected a much higher rate of adverse events for hospitalized patients than previous studies have shown.

“Without doubt, we’ve seen improvements in health care over the past decade, and even pockets of excellence, but overall progress has been agonizingly slow,” says Health Affairs Editor-in-Chief Susan Dentzer. “It’s clear that we still have a great deal of work to do in order to achieve a health care system that is consistently high-quality–that is, safe, effective, patient-centered, efficient, timely, and devoid of disparities based on race or ethnicity.”

–Warren S. Hersch