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Most Americans who go to the doctor will get a diagnosis that is wrong or late at least once in their lives, sometimes with terrible consequences, according to a report released Tuesday by an independent panel of medical experts.

This critical type of health-care error is far more common than medication mistakes or surgery on the wrong patient or body part. But until now, diagnostic errors have been a relatively understudied and unmeasured area of patient safety. Much of patient safety is focused on errors in hospitals, not mistakes in diagnoses that take place in doctors’ offices, surgical centers and other outpatient facilities.

The new report by the Institute of Medicine, the health arm of the National Academy of Sciences, outlines a system-wide problem. The report's authors say they don't know how many diagnostic errors take place. But the report cited one estimate that such errors affect at  least 12 million adults each year, or about 5 percent of adults who seek outpatient care.

"Despite the pervasiveness of diagnostic error and the risk for patient harm, they have been largely unappreciated within the quality safety movement in health care and this cannot and must not continue," said Victor Dzau, institute president, during a news briefing Tuesday.

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What’s more, errors will likely worsen because as the diagnostic process and the delivery of health care become more complex, according to the committee that conducted the study. The study is the institute's third in a series on patient safety. Its landmark 1999 report "To Err is Human" dramatically exposed the number of deaths--as many as 100,000 a year in hospitals--because of errors in medical treatment.

But that report and a subsequent one barely mentioned errors in the diagnostic process.

That's because it's hard to measure these mistakes.

“The data on diagnostic errors are sparse, few reliable measures exist and often the error is identified only in retrospect,” said John R. Ball, chair of the committee and executive vice president emeritus of the American College of Physicians. Sometimes that only happens after autopsies, or as a result of medical malpractice suits.

The stereotype of one physician making a wrong diagnosis is not always accurate, he said. Often it happens because of errors in the health care system. The solution requires nothing short of a fundamental overhaul of the entire process of how a diagnosis is made, the committee authors said.

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Experts say diagnosis is one of the most difficult and complex tasks in health care because it involves patients, clinicians, thousands of lab tests, and more than 10,000 potential diagnoses.

“It crosses so many different domains in the practice of medicine, which makes it complicated by itself,” said Paul Epner, executive vice president of the Society to Improve Diagnosis in Medicine, a nonprofit, physician-led organization patient safety group. The advocacy group petitioned the IOM to produce the report.

Diagnostic errors happen for many reasons, the committee found. There isn't enough collaboration among clinicians, patients and their families. Clinicians only get limited feedback about the accuracy of their diagnoses. The health-care culture discourages transparency and disclosure of errors.

The report cited the experience of one patient, identified only as Carolyn, who arrived in the emergency room with chest pain and pain down her left arm and other classic symptoms of a heart attack. But her tests were normal, and the clinician told her she had acid reflux. A nurse even told her to stop asking questions because the doctor "doesn't like to be questioned," the woman said in a video clip.

The woman was released but had to return two weeks later. She had to have a procedure to unblock her artery. And she did have a heart attack.

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The report also said that health information technology may be contributing to diagnostic errors. More doctors’ offices and health systems now have electronic health records, but clinicians often complain the systems are hard to use.

Doctors often don’t know when they have made the wrong diagnosis, said Tejal Gandhi, president of the National Patient Safety Foundation, and an internal medicine doctor for 15 years. If a doctor misses something and another one figures it out, the first doctor often never hears about it, said Kavita Patel, a health policy expert at the Brookings Institution's Center for Health Policy and a primary care doctor at Johns Hopkins Medicine.

The authors called for health-care organizations to put systems in place to identify diagnostic errors and near misses, adopt a non-punitive culture, and work as a team. Patel said one way to do that is for frontline workers, like medical assistants, to be empowered to act as a check and balance and raise flags, even if it's "something doctors won't like but will appreciate when they avoid a near miss."

Christine Cassel, president of the National Quality Forum and one of the committee authors, said doctors shouldn't feel embarrassed if they hear from a colleague who has diagnosed their patient with X instead of Y. Every physician should be open to getting that kind of feedback, she said.

Experts say patients can do a lot to help get the right diagnosis. Here is a checklist:

• Be clear, complete and accurate when you tell your clinician about your illness. When did symptoms begin? What made them better or worse? Jot down notes and bring them with you.

• Remember what treatments you've tried in the past, if they helped, and what, if any, side effects you had.

• Keep your own records of test results, referrals and hospital admissions. Keep an accurate list of your medications. Bring the list when you see your clinician or pharmacist.

• Remember to ask your clinician these three questions:

1. What could be causing my problem?

2. What else could it be?

3. When will I get my test results and what should I do to follow up?

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