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Although there is a general feeling that misdiagnosis is quite common, with many people giving anecdotal accounts of their own experiences, it is difficult to get exact data. Whereas there are many studies of adverse drug events and nosocomial infections, there is a relative lack of misdiagnosis studies.
A study of Patient Safety Incidents (PSIs) by HealthGrades found that "Failure to Rescue", meaning failure to diagnose and treat in time, was the most common cause of a patient safety incident, with a rate of 155 per 1,000 hospitalized patients. Unfortunately, the study did not further break down statistics into the types of misdiagnosis, delayed diagnosis or other factors. 1
The National Patient Safety Foundation (NPSF) commissioned a phone survey in 1997 to review patient opinions about medical mistakes. Of the people reporting a medical mistake (42%), 40% reported a "misdiagnosis or treatment error", but did not separate misdiagnosis from treatment errors. Respondents also reported that their doctor failed to make an adequate diagnosis in 9% of cases, and 8% of people cited misdiagnosis as a primary causal factor in the medical mistake. Loosely interpreting these facts gives a range of 8% to 42% rate for misdiagnoses.
Misdiagnosis rates in the ICU or Emergency Department have been studied, with rates ranging from 20% to 40%. These misdiagnosis rates are likely to be higher than the overall health care misdiagnosis rate because of the time-critical and serious nature of the diagnosis under these crisis conditions.
Malpractice and misdiagnosis: Another interesting fact is that a large proportion of malpractice cases are based on misdiagnosis or delayed treatment of serious conditions. Davenport (2000) lists the top five malpractice-risk conditions in order of prevalence as myocardial infarction, breast cancer, appendicitis, lung cancer and colon cancer, and notes that almost all suits are cases of misdiagnosis or mismanaged diagnostic tests leading to delayed treatment. Myocardial infarction and appendicitis are likely to be related to emergency department visits, whereas the three litigation-prone types of cancers are more common in general physician work.
Misdiagnosis in the emergency department: The rates of misdiagnosis in the emergency department or ICU have been studied. The majority of lawsuits involved the ED and of these, the majority involved delayed treatment and therefore presumably related to misdiagnosis. One study found a rate of 20% of misdiagnosis in the ICU. Other studies have found that it is relatively common for serious conditions such as acute myocardial infarction (heart attack), stroke, pulmonary embolism, meningitis, or appendicitis to be misdiagnosed in emergency care. For example, non-typical presentations such as a young person or a woman having a heart attack are less likely to be correctly diagnosed. Furthermore, an ECG test does not rule out a heart attack even if it is normal, and some physicians rely too heavily on this test.
Appendicitis is another common and serious misdiagnosis in the ED. Initial misdiagnosis rates of appendicitis in children are high, ranging from 28% to 57% under 12s to almost 100% misdiagnosis for appendicitis in infants (Rothrock et al, 2000).
Misdiagnosis and biopsy: Pathology slide tests involve a workup of a sample onto a slide and then a manual viewing by a pathologist, or more commonly a technician. They are commonly used to identify abnormal cells, such as in cancers. This inherently human process has a clear risk of error and can lead to misdiagnosis. For example, in a December 1999 study of 6,171 slides, Johns Hopkins Hospital in Baltimore found a 1.4% error rate in pathology tests in patients referred for cancer treatment. Of the 86 total misdiagnoses, 20 had benign tumors misdiagnosed as malignant and presumably received unnecessary cancer treatment. An earlier Johns Hopkins study of prostrate cancer biopsies found an error that ruled out cancer in six out of 535 cases.
Misdiagnosis and autopsy studies: One useful way to detect misdiagnosis is to perform an autopsy, and then compare the original diagnosis with that found at autopsy. Various studies have found major differences, with discrepancy rates as high as 40% in the Medical ICU (CHEST, February 2001). This rate of 40% in the ICU is undoubtedly higher than the rate for general medicine because of the difficult and often multifactorial nature of serious ICU cases. Unfortunately, autopsy rates are declining for various reasons and the opportunity to measure misdiagnosis in this way is reduced.
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