Understanding Diagnostic Errors
A diagnostic error, which involves a missed, delayed, or wrong diagnosis, can mean the difference between life and death for a patient because of the potential for delayed, incorrect, or lack of treatment for a possibly serious condition.
Diagnostic error is a major source of preventable harm in US healthcare. Although diagnostic errors are difficult to measure, it is estimated that each year approximately 12 million US adults experience outpatient diagnostic errors—about half of which may cause patient harm—and an estimated 795,000 Americans die or are permanently disabled every year due to misdiagnosis.
Diagnostic errors can also be costly. An analysis of 226,781 paid malpractice claims from 1999–2018 found that diagnosis-related allegations were the second highest proportion of malpractice allegations, accounting for 26.6% of claims, with a median payment per claim of $285,000. Failure to diagnose, delay in diagnosis, wrong or misdiagnosis, and failure to order the appropriate test rank among the leading specific malpractice allegations.
Diagnostic errors have been included in some form in almost every iteration of ECRI's Top 10 Patient Safety Concerns. Most recently, diagnostic errors were included in the list for 2025 regarding the missed diagnosis of the "Big Three."
Misdiagnosis of the 'Big Three'
The most serious diagnostic errors may be attributed to conditions known as the "Big Three." Misdiagnosis of cancers (37.8%), vascular events (22.8%), and infections (13.5%) account for most high-severity cases, based on closed malpractice claims.
The most common conditions in each category, as of the publication of the study, were lung cancer, stroke, and sepsis, respectively. Other commonly misdiagnosed conditions include breast, colorectal, prostate, and skin cancers; heart attack; aortic aneurysm and dissection; meningitis and encephalitis; pneumonia; and endocarditis.
Most diagnostic errors in this analysis took place in outpatient care settings where the majority of claims were related to missed cancer diagnoses. In emergency departments, missed vascular events and infections were higher than cancer diagnostic errors.
Among high-severity harm cases discussed in the study, "there were 26,506 specific causal factors identified; only...2.5% of cases had no risk management issues identified." Overall, the analysis found that the three most common causal factors were clinical judgment factors (85.7%), communication factors (34.9%), and clinical systems (22.0%).
Clinical judgment factors included "failure or delay in ordering a diagnostic test; failure to establish a differential diagnosis; failure to appreciate relevant symptoms, signs, or test results; failure or delay in obtaining consultation or referral; or misinterpretation of diagnostic studies." Communication factors included failure in provider-provider and provider-patient communication about the patient's condition, failure to read the medical record, failure to communicate follow-up instructions, and poor rapport with patient. Lastly, clinical system factors included "patients not receiving results...failure to follow up on a new finding...failure or delay in completing recommended diagnostic tests, clinician not receiving test results, and failure to identify provider coordinating care."
While much of the data about harm events is found in closed malpractice claims, these claims capture only a small fraction of preventable harm—estimates suggest that "only about 1.5% of medically negligent care events result in a malpractice claim." Claims data also tend to be skewed toward more severe outcomes, since the likelihood of a claim is more closely tied to the extent of harm than to the presence of care process failures.
Improving Diagnostic Accuracy
There is a widely held misconception that diagnosis is a single happening discretely limited in time. However, the diagnostic process is a complex, multifaceted progression that involves many people, over multiple periods, in multiple settings.
Another misconception about diagnosis is that little can be done to significantly improve it—to err is, after all, human. However, although difficult, it is possible to improve diagnostic accuracy.
Address System-Level Factors
Recognizing the multifaceted nature of diagnostic error is key; it is not always the result of individual oversight but often stems from complex interactions among several system-level factors in the internal and external environment (see Figure 1).
Figure 1
Electronic health record (EHR) challenges. A lack of access to a patient's full medical history—due to fragmented systems, poor interoperability of the EHR, or care occurring across multiple institutions—can make it harder for clinicians to make informed diagnostic decisions. Clinical staff, informaticists, information technology personnel, and health technology vendors should collaborate to build the EHR so clinicians and staff can readily understand the development of the patient's clinical story: the trajectory of the patient's condition, examinations and tests that have been performed, and diagnoses that have been considered.
Time constraints. Physicians are often expected to see a high volume of patients in a limited amount of time, which may compromise the diligence of clinical evaluations. When rushed, providers may rely more heavily on cognitive shortcuts and bias, increasing the risk of diagnostic error. Optimizing workflow, leveraging team-based care, and allowing adequate time for complex cases can help alleviate some of this pressure.
Staff shortages. Inadequate staffing can lead to delay in care, reduced or inadequate communication, and overburdened clinicians. Addressing this issue requires strategic investments in workforce planning, retention initiatives, and support systems that reduce clinician burnout.
Organizational culture. The organization's culture should support open discussion of the diagnostic process and learning from diagnosis-related events. A supportive culture also encourages nonpunitive reporting and discussion of missed or delayed diagnoses so that clinicians may recognize similar situations before they lead to harmful events.
Organizations should also institute a peer support program—such as "care for the caregiver" programs—for clinicians involved in patient harm resulting from a diagnostic error.
Mitigate Cognitive Biases
Diagnostic error frequently stems from cognitive bias rather than a lack of clinical knowledge. Although difficult to quantify, it is estimated that between 36% and 77% of diagnostic errors could be the result of cognitive bias. For instance, premature closure occurs when a physician prematurely suggests a diagnosis based on initial symptoms and ignores new data that suggests an alternative explanation.
Education on cognitive bias and the diagnostic process can help illustrate how often mental shortcuts are taken and can include techniques for avoiding common cognitive traps. Through case-based learning, simulation, and reflective practice, healthcare providers can learn to identify when cognitive shortcuts may be impacting diagnostic accuracy. A 2016 systematic review found evidence that considering differential diagnoses, engaging in metacognition (i.e., thinking about the diagnostic thought process), taking a diagnostic time-out, and seeking other viewpoints can improve clinicians' diagnostic reasoning in simulated settings.
Lastly, providing regular, structured feedback may help clinicians improve their diagnostic performance.
Reduce Health Disparities
When patient characteristics such as race, language, income, disability, or access to transportation are not meaningfully integrated into care planning, it can lead to delays in care, reduced care quality, and worse health outcomes.
For example, women whose pain symptoms are routinely diminished may internalize that message and later downplay the severity of their symptoms to their provider, leading to delayed or missed treatment.
Providing culturally responsive services to patients is an effective strategy to reduce disparities in care. Organizational leaders should provide care teams with education that addresses diverse cultural needs and policies that make a patient’s identity a central component of their care plan. Qualified medical interpreters and written information provided in the patient’s preferred language should be used when necessary.
Outpatient clinics can expand their operating hours and appointment times. Scheduling staff should group a patient’s associated appointments, such as routine visits and diagnostic testing, or allow patients to self-schedule. Clinics can partner with transportation services to offer group rides or subsidized services.
Engage Patients and Families
Engaging patients and their families in the diagnostic process is a crucial component of delivering safe, effective, and patient-centered care. Prior to an appointment, providing tools such as checklists or symptom trackers can give patients a sense of control and ensure that critical information is shared during appointments. Patients should also be encouraged to prepare for medical visits by writing down symptoms, concerns, and questions in advance.
During appointments, clinicians should use plain language, avoid medical jargon, employ the "teach-back" method to ensure comprehension, and tailor communication and educational materials to meet individual patient needs. Encouraging patients to ask questions—such as "What else could this be?"—helps create a two-way dialogue and signals to patients that their voice is an important part of the diagnostic process.
Digital tools such as patient portals can further enhance patient engagement. These platforms allow patients to review test results, track appointments, and send messages directly to their care team. For example, patients may notice missing or out-of-range test results and question their providers about them. When used effectively, patient portals can reduce communication gaps, provide patients with timely access to their health information, and promote continuity of care. Patients may need support in navigating these tools, especially if they are not tech-savvy or face language barriers.
Transparent communication throughout the diagnostic process builds trust and strengthens the patient-provider relationship. Dismissing or minimizing patient concerns and symptoms—also called "medical gaslighting"—erodes trust and may contribute to diagnostic error.
Candor regarding diagnostic uncertainty, potential next steps, and the reasoning behind clinical decisions invites collaboration and helps patients feel valued and informed. Families and caregivers can also play a key role, particularly when patients need support in understanding complex information.
Discharge instructions should include diagnostic test results to better support continuity of care. Instructions should clearly inform patients how to continue their care at home, new symptoms to watch for, and what to do if problems arise. Providers involved in the patient's follow-up care should also receive discharge instructions and diagnostic test results.