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Since its inception, the patient safety movement has emphasized medication errors, handoff errors, communication and teamwork errors, healthcare-associated 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. Until recently, diagnostic errors have been less well emphasized, in part because they are more difficult to measure and to fix.

Interestingly, diagnostic errors were underemphasized from the very beginning of the patient safety movement.1 In the landmark Institute of Medicine (IOM) report To Err Is Human,2 the term “medication errors” is mentioned 70 times, while the phrase “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) and continue to account for a significant amount of preventable harm to patients. A review of malpractice claims data in the United States for the period from 1986 through 2010 found that out of 350,706 paid claims, diagnostic errors accounted for almost one-third of claims and the highest amount of total payments.4 Another estimate suggests that diagnostic error affects 12 million adult outpatients every year in the United States.5

As the field of patient safety evolves, the momentum for addressing the problem of diagnostic error—now viewed as a critical patient safety issue—is growing.6,7 In response, in 2015 the National Academy of Medicine (NAM, formerly the IOM) released another landmark report entitled Improving Diagnosis in Health Care. The report concludes that the vast majority of patients will experience a diagnostic error at some point and suggests that greater collaboration among stakeholders is required to mitigate the problem.8 The report also emphasizes the need for accurate measurement of diagnostic error and outlines opportunities to improve the diagnostic process and reduce error.

At first glance, diagnostic errors would seem to represent human failings—pure lapses in cognition. And it is true that, perhaps more than any other area in patient safety, the training and skills of the clinician 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, we 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 ...

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