Roughly 12 million adults who visit U.S. doctors’ offices and other outpatient settings, or one in 20, are misdiagnosed every year, a new study has found, and half of those errors could lead to serious harm.

The study by a team of Texas-based researchers attempted to estimate how often diagnostic errors occur in outpatient settings such as doctors’ offices and clinics, as exact figures don’t exist. The team’s study will be published this month in the British medical journal BMJ Quality & Safety.

Efforts to improve patient safety have largely focused on inpatient hospital care, including programs introduced by President Barack Obama’s Affordable Care Act, even though most diagnoses are made in outpatient clinics, the study said.

“It’s important to outline the fact that this is a problem,” said Dr. Hardeep Singh, the study’s lead author and a patient safety researcher at Baylor College of Medicine in Houston and at the Michael E. DeBakey VA Medical Center, also in Houston.

“Because of the large number of outpatient visits, this is a huge vulnerability. This is a huge number and we need to do something about it,” he said in an interview with Reuters.

To explore the issue, researchers combined data from three past studies to generate a sample pool of about 3,000 medical records. Their analysis found a misdiagnoses rate of just over 5 percent, which when extrapolated to the 80 percent of U.S. adults that receive outpatient care every year, comes to 12 million people.

Researchers added that faulty medical records and other potential flaws in the data could mean the error rate is even higher. Previous research done by Singh has suggested that many of these misdiagnoses could lead to serious problems, such as delayed cancer treatments or, conversely, unnecessary treatment of nonexistent problems.

“Not all misdiagnoses lead to any severe harm, but many do,” Singh said. “We can extrapolate that almost half of these could cause some amount of severe patient harm.”

Singh said he hopes the research helps foster discussion of misdiagnoses and patient safety in outpatient settings by providing lawmakers, patient advocates and healthcare organizations with a clearer sense of the problem.

“Measuring the problem is the first step to actually trying to fix it,” he said.

(Editing by Barbara Goldberg; and Peter Galloway)

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By Curtis Skinner