A new study finds that many Americans are misdiagnosed in outpatient clinics, but researchers believe that if patients and physicians work together, the high rates of misdiagnosis will decline.

A new study, published in BMJ Quality and Safety, finds that one in every 20 adults in the U.S.—which translates to about 12 million adults—is misdiagnosed in outpatient clinics every year. What’s more, many of these misdiagnoses have the potential to cause serious harm.

According to the Society to Improve Diagnosis in Medicine, diagnostic error is the leading cause of medical malpractice claims in the U.S., and is estimated to cause 40,000 to 80,000 deaths annually.

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The data sources in the new study included two previous studies that used electronic triggers, or algorithms, to detect unusual patterns of return visits after an initial primary care visit, or lack of follow-up after abnormal clinical findings related to colorectal cancer—both suggestive of diagnostic errors. A third study examined consecutive cases of lung cancer.

In all three studies, diagnostic errors were confirmed through chart review and defined as missed opportunities to make a timely or correct diagnosis based on available evidence.

In a previous study, the researchers looked at the likelihood of these misdiagnoses inconveniencing patients or leading to severe disability, and found that almost half of the misdiagnoses would be harmful to the patient.

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Lead study author Dr. Hardeep Singh, patient safety researcher at the Veterans Affairs Center for Innovations in Quality, Effectiveness and Safety, at the Michael E. DeBakey VA Medical Center in Houston and an associate professor at Baylor College of Medicine, told Healthline that there are several reasons why misdiagnosis rates are high. “For physicians, there are several issues, such as how they make decisions and how they handle uncertainty. When a patient comes in with a lot of undifferentiated symptoms, in primary care the diagnosis evolves over time and you might start with a certain work-up, but that changes,” said Singh.

Singh went on to say that physicians should make patients more aware of how things will evolve and what patients need to do. “Some of the follow-up issues are important too. When people have abnormal findings, we need to ask, how do we track them better over time? If they had an abnormal test, patients need to ask, How do I get informed? When is my next test scheduled?” said Singh.

Which diseases represent the highest number of misdiagnoses? In addition to cancer, Singh said that common symptoms are often missed in common diseases, such as decompensated heart failure in patients, pneumonia, anemia, spinal cord compression, and kidney failure.

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What can a patient do to prevent a misdiagnosis? Singh advised patients to be proactive by providing physicians with a list of their symptoms and their medical problems. Patients should also have access to all the information.

“We are going to need to have more engagement and empowerment in patients in order to take this issue forward. We cannot do this without having more patient participation in this process. If I express uncertainty that your diagnosis is bronchitis, and you may also have heart failure, then if you get swelling in the legs or your breathing gets worse, I want you to come back and see me tomorrow or the day after. We want doctors to express uncertainty, but we also want patients to come back and see us,” said Singh.

Finally, Singh told Healthline, “This has to be a multi-faceted effort involving physicians, their care teams, patients, and the healthcare system where we practice. Everybody plays a role. Not all misdiagnoses are going to lead to problems. You do get problems when there’s a delay in needed treatment and when you get unnecessary tests, but it’s obviously not good to get misdiagnosed for any reason.”

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