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Diagnostic Errors: The “Big Three” That Account for 75% of Errors

Dec 22, 2020 07:00AM ● By Med Magazine

By COPIC’s Patient Safety and Risk Management Department

In the world of medical liability, we know that diagnostic errors are an issue. However, the scope of the problem is uncertain, as national estimates about diagnostic errors that cause substantial harm can range from 40,000 to four million each year. When examining this topic, a good starting point is to define what constitutes this type of error.

A Johns Hopkins research team contributed important information on this topic that appeared in Diagnosis1. Utilizing a database from CRICO (the professional liability insurance company for Harvard medical institutions), they analyzed more than a quarter of all medical liability claims made in the US over the span of a decade. Surprisingly, in a world where there is the theoretical diagnostic possibility of over 10,000 human illnesses, the research team found that a majority of cases where serious harm occurred (75% of diagnostic errors) were connected to only 15 diseases in these three categories:

  1. Vascular events (e.g., stroke, heart attack, pulmonary embolus, etc.)

  2. Infections (e.g., sepsis, meningitis, appendicitis, etc.)

  3. Cancers (e.g., lung, colon, breast, etc.)

They called these areas the “Big Three.” Approximately half of these errors resulted in serious injury, and the other half caused death. It was noted that 71% of these occurred in either the ED setting or outpatient clinics. 

The Big Three are not evenly distributed across specialties or patients—missed vascular events are most common in emergency care, missed infections are most important among children, and missed cancer diagnoses lead the way in primary care.

Table 1: Proportion of serious harms attributed to “The Big Three” in frontline care settings2


These results are consistent with COPIC’s historical claims data. For the last two decades, we have spoken and written on the “big risks” for primary care—heads, hearts, bellies, bugs, and cancer. We found that over two-thirds of claims against primary care fall into these categories. In addition, our data shows that misdiagnoses were the most common, catastrophic, and costly medical mistakes. This closely reflects the “Big Three” data. For example, their vascular is COPIC’s “heads and hearts,” and our “bellies” is encompassed in appendicitis (infection) and ischemic colitis (vascular).

The National Academy of Medicine outlined a broad range of research topics to help make progress on improving diagnostic accuracy, and it clearly emphasized that early wins may be achieved through an initial focus on “identifying the most common diagnostic errors, ‘don’t miss’ health conditions that may result in patient harm, [and] diagnostic errors that are relatively easy to address.”

Table 2: Exemplars from each “Big Three” category with diagnostic error causes and possible solutions2

Diagnostic errors are common and a frequent cause of litigation. The human toll on both patients and physicians is substantial and underappreciated. The Big Three article is an important contribution to the diagnostic error literature, and at COPIC we have found that our experience is very similar. We continue to look at resources and tools that will help improve outcomes in this area and educate our insureds on ways to further improve patient safety.