A recent study of the American health care system has revealed a shocking statistic: Each year, roughly 12 million adults that visit U.S. doctors’ offices and other outpatient settings are misdiagnosed. With about 80 percent of the adult population seeking medical advice every year, this means that one in about every 20 patients is diagnosed with the wrong illness. Possible consequences from this misdiagnosis include serious health problems due to delayed or unnecessary treatment.

The study was conducted by a team of Texas-based researchers and will be published later this month in the British Medical Journal Quality & Safety. The study attempted to estimate how often diagnostic errors occurred in outpatient settings such as a doctors' offices and clinics. According to the data, efforts to improve patient safety have largely focused on inpatient hospital care, including programs introduced by the Obama administration’s Affordable Care Act. Most diagnoses are made in outpatient clinics. Dr. Hardeep Singh, the study’s lead author, emphasized how the importance of outlining the facts of this problem. “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,” Singh told Reuters in an interview.

The study combined data from three past studies to create a sample pool of about 3,000 medical records. After careful analysis, it was revealed that there was a misdiagnosis rate of just over five percent. When putting that into context, about 80 percent of American adults receive outpatient care every year. This means that 12 million people are misdiagnosed on a yearly basis. Researchers believe that faulty medical records and other possible flaws in the data could make the error rate even higher.

Possible consequences of these misdiagnoses are serious problems such as delays in lifesaving treatment or receiving unnecessary treatment for problems that don’t exist. “Not all misdiagnoses lead to any severe harm, but many do. We can extrapolate that half of these could cause some amount of sever harm,” Singh concluded to Reuters. The researchers hope that the results of their work will raise awareness for misdiagnoses and patient safety in outpatient settings by giving lawmakers, patient advocates, and health care organizations a more clear sense of the problem.