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The modern patient safety movement has emphasized medication errors, handoff errors, infections, and surgical errors; all of these areas are amenable to technological (e.g., computerized order entry), procedural (e.g., double checks), and policy (e.g., “sign-your-site”) solutions. Diagnostic errors have been less well emphasized, in part because they are more difficult to measure and to fix.

Interestingly, this relative inattention to diagnostic errors began from the very start of the patient safety movement.1 In the landmark Institute of Medicine report To Err is Human,2 the term “medication errors” is mentioned 70 times, while “diagnostic errors” comes up only twice. This is ironic, since diagnostic errors accounted for 17% of preventable errors in the Harvard Medical Practice Study,3 the source of the IOM estimate of 44,000 to 98,000 yearly deaths from medical mistakes (the “jumbo jet a day” figure that helped launch the safety movement; Chapter 1). A systematic review of autopsy studies conducted over four decades found that nearly 1 in 10 patients suffered a major antemortem diagnostic error, a figure that has fallen only slightly (the best recent estimate is about 5%) despite all of today's advanced imaging and laboratory techniques.4 Diagnostic error remains the most common reason for a paid malpractice claim in ambulatory patients.5

At first glance, diagnostic errors would seem to represent human failings—pure failures of cognition. And it is true that, perhaps more than any other area in patient safety, the training and skills of the diagnostician remain of paramount importance. However, in keeping with our modern understanding of patient safety, there are system fixes that can decrease the frequency and consequences of diagnostic mistakes. In this chapter, I will discuss the cognitive as well as the process failures (such as failure to transfer the results of a crucial laboratory or radiologic study to the correct provider in a timely way) that give rise to diagnostic errors.

Annie Jackson, a 68-year-old African-American woman with mild diabetes, high blood pressure, and elevated cholesterol, presented to the emergency department after 30 minutes of squeezing chest discomfort. An ECG was quickly obtained. The ER physician, Dr. Zoe Bennett, studied the tracing and saw some nonspecific changes in the ST and T segments—not entirely normal but not the ST-segment elevations that are classic for acute myocardial infarction (MI). On exam, she found mild tachycardia, clear lungs, and mild tenderness over the lower part of the patient's sternum. She considered the latter discovery quite reassuring (after all, such tenderness would be more characteristic of a musculoskeletal process than a heart attack), but also ordered a troponin (a biomarker released by damaged heart cells). It came back mildly elevated, again not in the range specific for MI but not normal either. Nevertheless, she made a diagnosis of costochondritis (inflammation of the sternum–rib joint), prescribed an anti-inflammatory agent and bed rest, and released Ms. Jackson from the emergency department. She died ...

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