Diagnostic Error

Diagnostic Error

Common, Costly, and Harmful

Diagnostic error is one of the most important safety problems in health care today, and inflicts the most harm. An estimated 40,000 to 80,000 patients die annually in the U.S. from diagnostic errors. Diagnostic errors are the most common cause of medical errors reported by patients and researchers have found that diagnostic errors—not surgical mistakes, or medication overdoses—account for the largest fraction of malpractice claims, the most severe patient harm, and the highest total of penalty payouts.


What is Diagnostic Error?

The National Academy of Medicine (formerly the Institute of Medicine [IOM]) defined diagnostic error as the failure to (a) establish an accurate and timely explanation of the patient’s health problem(s) or (b) communicate that explanation to the patient. Simply put, these are diagnoses that are delayed, wrong, or missed altogether.

These categories overlap, but examples help illustrate some differences:


  • A delayed diagnosis refers to a case where the diagnosis should have been made earlier. Delayed diagnosis of cancer is by far the leading entity in this category. A major problem in this regard is that there are very few good guidelines on making a timely diagnosis, and many illnesses aren’t suspected until symptoms persist, or worsen.
  • A wrong diagnosis occurs, for example, if a patient truly having a heart attack is told their pain is from acid indigestion. The original diagnosis is found to be incorrect because the true cause is discovered later.
  • A missed diagnosis refers to a patient whose medical complaints are never explained. Many patients with chronic fatigue, or chronic pain fall into this category, as well as patients with more specific complaints that are never accurately diagnosed.


“It is likely that most of us will experience at least one diagnostic error in our lifetimes, sometimes with devastating consequences.”

Improving Diagnosis in Health Care. Institute of Medicine, 2015

Why Diagnostic Errors Occur

People may assume that diagnostic errors result from sub-optimal care. While this cause is possible, rarely does it explain the problem. Much more commonly, diagnostic error stems from the complexity of the diagnostic process, complexities in how health care is delivered, and the same kinds of cognitive errors that we all make in our everyday lives. Most diagnostic errors are made by conscientious clinicians practicing in first-rate medical organizations.

Complexity of the diagnostic process  Diagnosis is not just an endpoint; it's a very complex process. There are over 10,000 known diseases and 5,000 kinds of laboratory tests. But there is only a small number of symptoms, so that any one symptom may have dozens or hundreds of possible explanations. Diagnostic testing may be helpful to clarify the problem, but often it is simply a matter of observing the clinical course, which takes time. An error may occur at any step of the process--while getting a complete patient history, doing an appropriately thorough examination, obtaining the right tests, or interpreting tests correctly.

Complexity in healthcare delivery  Healthcare systems link hundreds of different processes, practices, procedures, and technologies to deliver safe and accurate diagnoses. While medical systems are built with patient safety in mind, the complexity of our health care can cause the baton to drop, despite everyone’s best effort.

Many diagnostic errors involve breakdowns in communication and coordinating care, or other problems in our healthcare systems. Test results can get lost, subspecialty consultation may not be available in a timely manner, or testing equipment may be malfunctioning. Our healthcare systems grow more complicated by the day, and care is delivered in many different settings.

Cognitive errors  Doctors are human and make the same kinds of mental errors we all make in our every day lives. Sometimes we don’t notice a key finding, or we misinterpret what was said. We may jump to conclusions, or fail to consider whether there might be a better answer than our first idea. We think we’ve made sense of the situation, but we’re wrong. For example, although a stomach ailment may be the explanation for a patient’s abdominal pain, the same pain can be mimicked by vascular or neurologic conditions that don’t immediately come to mind. 

More information about cognitive bias can be found here.


Diagnostic Error: A Patient Safety Imperative

Accurate and timely diagnosis are the two cornerstones of high-quality patient care. Harm can result from diseases that aren’t treated at an early stage, or if treatment isn’t appropriate for the condition you have.

Patients can help avoid diagnostic errors by becoming more knowledgeable about the diagnostic process, and taking advantage of tools, like the ones offered here. Engaged patients have the best outcomes. The IOM recommends that patients become full partners in their own care, and patients can be an important safety net in catching diagnostic errors before they lead to harm.

Physicians can help avoid diagnostic errors by better understanding the cognitive errors that can commonly occur, and being especially careful navigating their healthcare systems and resources. Stop to think, use decision support resources, be mindful and reflective, and make the patient your partner in the diagnostic process. Resources for physicians are located here.


“Improving the diagnostic process is not only possible, but it also represents a moral, professional, and public health imperative.”

Improving Diagnosis in Health Care. Institute of Medicine, 2016

Society to Improve
Diagnosis in Medicine
1501 Hinman Ave, #7B
Evanston, Il 60201