This figure amounts to 1 out of 20 adult patients, and researchers say in half of those cases, the misdiagnosis has the potential to result in severe harm.
Previous studies examining the rates of medical misdiagnosis have focused primarily on patients in hospital settings. But this paper suggests a vast number of patients are being misdiagnosed in outpatient clinics and doctors' offices.
"It's very serious," says CBS News chief medical correspondent Dr. Jon LaPook. "When you have numbers like 12 million Americans, it sounds like a lot -- and it is a lot. It represents about 5 percent of the outpatient encounters."
Getting 95 percent right be good on a school history test, he notes, "but it's not good enough for medicine, especially when lives are at stake."
For the paper, the researchers analyzed data from three prior studies related to diagnosis and follow-up visits. One of the studies examined the rates of misdiagnosis in primary care settings, while two of the studies looked at the rates of colorectal and lung cancer screenings and subsequent diagnoses.
To estimate the annual frequency of misdiagnosis, the authors used a mathematical formula and applied the proportion of diagnostic errors detected in the data to the number of all outpatients in the U.S. adult population. They calculated the overall annual rate of misdiagnoses to be 5.08 percent.
"Although it is unknown how many patients will be harmed from diagnostic errors, our previous work suggests that about one-half of diagnostic errors have the potential to lead to severe harm," write the authors in their study. "While this is only an estimate and does not imply all those affected will actually have harm, this risk potentially translates to about 6 million outpatients per year."Lead author Dr. Hardeep Singh, of the Baylor College of Medicine and the Michael E. DeBakey Veterans Affairs Medical Center in Houston, has previously conducted other studies that examine the reasons for misdiagnosis.
Singh's 2012 study also offered a snapshot of the symptoms doctors most frequently miss or misdiagnose. The top complaints that turned out to be symptoms of more serious conditions were cough, abdominal pain and shortness of breath.
"The art of medicine is trying to figure out which of these symptoms -- which 99 times out of 100 is something innocent, one time out of 100 turns out to be something serious," says LaPook. "That's the art of medicine. That's the tricky part."
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