At least one in 20 adult outpatients misdiagnosed in U.S. every year

Half of these errors could be potentially harmful, say the authors, who add that their findings should prompt renewed efforts to monitor and curb the numbers of misdiagnoses.

To date, patient safety improvements have largely focused on hospital stays and issues such as infections, falls, and medication errors, say the authors. But most diagnoses are made in outpatient clinics, where patients are looked after by several different healthcare teams and few safety concerns are ever reported.

And because there are no reliable estimates of how common misdiagnoses are, it has been difficult to prioritize strategies to reduce them, they add.

In a bid to gauge the numbers of diagnostic errors made in US outpatient clinics every year, the authors combined data from several published studies, involving hundreds of medical records, sampled from a large pool of outpatient clinic visits.

This approach overcomes many of the challenges inherent in making similar assessments from malpractice data, autopsy reports, or specialized fields of medicine, say the authors.

The records were reviewed in detail to see if a diagnostic error had been made. The proportion of errors found was then applied to the larger population of all outpatient visits and then to the US adult population as a whole to estimate the annual frequency of misdiagnoses.

Based on these data, the authors calculated the numbers of new cases of misdiagnoses at 5.08%, suggesting that at least 1 in 20 US adults is misdiagnosed every year. And around half of these mistakes could potentially be harmful, if previous research is anything to go by, they say.

If these figures are applied to the US population as a whole, this works out at around 12 million adults each year.

Healthcare organizations, patient advocates, policymakers, and researchers should use the findings to push for further strategies to improve patient safety in this area, conclude the authors.