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Accurate diagnosis is the foundation upon which all treatment rests. A doctor cannot prescribe the right medicine or procedure unless she knows what is wrong with her patient.

That is why the results of a recent study in JAMA Internal Medicine (online, Aug. 26, 2013) are so chilling. Researchers tested more than 100 internists on their diagnostic accuracy. The volunteer physicians were presented with four case vignettes. Two were considered relatively easy, and two were categorized as difficult. In addition to assessing the accuracy of the final diagnosis, the investigators also questioned the participants on their confidence in their decisions.

In this study, 55 percent of the doctors who participated got the correct diagnosis on the two easier cases. Fewer than 6 percent of the internists accurately diagnosed the more difficult cases. The researchers note, “The overall diagnostic accuracy was rather low – 31 percent across the 4 cases.”

We think “abysmal” might be a better adjective. Any high school student who got only 31 percent of the answers correct on a test would flunk. Even though this was a study, lives hang in the balance when doctors miss a diagnosis.

The most shocking aspect of this study had to do with confidence. Despite the fact that more than 90 percent of the participants incorrectly diagnosed the difficult cases, they still were surprisingly confident about their diagnostic acumen. Confidence was rated on a scale from zero to 10, with zero being the lowest and 10 the highest. The average confidence on the easy cases was 7.2. On the more difficult cases, confidence levels averaged 6.4, even though most doctors missed the diagnosis.

Many readers of this column have shared stories about misdiagnoses. This one is particularly tragic: “My father died as a result of a missed diagnosis. He was in the coronary intensive care unit at a teaching hospital after suffering a heart attack. He was treated first at a community hospital, then transferred to the teaching hospital for angiography. While waiting for the cardiac surgeon to review the test results, and while on anticoagulants, my father developed knee swelling and pain in the leg used for the angiography. He was treated for days with narcotic painkillers for sciatica, which only made him constipated.

“No one noticed that he was bleeding massively into his abdomen. Lab results demonstrating the blood loss were ignored. Six days after the angiogram, while straining on a bedside commode, he had another cardiac event. Hours later, an attending physician finally saw the lab evidence of massive blood loss and ordered blood transfusions. Inexplicably, my father did not get the transfusion until many hours later after his heart muscle was irretrievably damaged. He went into cardiac arrest and died the day before he had been scheduled to go home.

“How do I know all this? Because I am a physician, I requested the chart. The nurses’ notes and lab results told the real story. Most families will never find out about diagnostic errors. They have no way to learn the truth.”

We offer advice on how to avoid diagnostic errors on our website (www.PeoplesPharmacy.com). If patients take a more active role in the diagnostic process, they may be able to reduce the likelihood of such terrible mistakes.

Joe Graedon is a pharmacologist. Teresa Graedon holds a doctorate in medical anthropology and is a nutrition expert. Their syndicated radio show can be heard on public radio. In their column, Joe and Teresa Graedon answer letters from readers. Write to them via their website: www.PeoplesPharmacy.com.