How Diagnostic Errors Happen in Medicine

The question of why diagnostic errors occur is one of the more important questions in modern medicine. Diagnostic errors affect millions of patients each year, contribute to substantial mortality, and produce significant suffering and additional cost. Yet most errors are not the result of incompetent care or simple negligence. They arise from a combination of factors involving the inherent difficulty of diagnosis, characteristics of human cognition, system-level features of healthcare delivery, and various other elements that interact in complex ways.

Understanding how diagnostic errors happen matters for several reasons. For patients, awareness supports informed engagement with care, including reasonable consideration of when additional evaluation is warranted. For clinicians, understanding common patterns supports approaches that reduce errors. For the healthcare system more broadly, recognizing the factors contributing to errors supports investments in approaches that reduce them, including process improvements, technological support, and various other interventions.

The diagnostic process is not a single decision but a structured sequence of activities. It begins with the patient's presentation and history, includes physical examination and various investigations, involves clinical reasoning to integrate the information, and concludes with diagnosis communicated to the patient and used to guide treatment. Errors can occur at any point in this sequence, with the cumulative effect determining whether the final diagnosis is correct.

This article explains how the diagnostic process actually works, identifies where errors typically occur, discusses the cognitive and system factors that contribute to errors, and frames how improvements in diagnostic accuracy can be achieved.

For more on misdiagnosis broadly, see How Often Do Doctors Misdiagnose Patients?.

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The Diagnostic Process

Understanding how the diagnostic process actually works helps frame how errors occur.

Initial Patient Presentation

The diagnostic process begins when a patient presents with symptoms or concerns. The initial presentation includes the patient's description of symptoms, their concerns, the timeline of events, and various other elements.

The quality of this initial information affects subsequent evaluation. Patients who provide comprehensive accurate information support better evaluation than those who provide incomplete or inaccurate information. The clinician's skill in eliciting comprehensive information matters substantially.

History Taking

The history taking expands on the initial presentation. The clinician asks about specific symptoms, prior medical history, family history, medications, social factors, and various other elements.

Comprehensive history taking supports accurate diagnosis. Limited history taking can miss information that would point to specific diagnoses. Inadequate history is one of the more common contributors to diagnostic errors.

Physical Examination

Physical examination provides additional information. The findings on examination, when integrated with history, support narrowing of the differential diagnosis.

Modern medical practice sometimes underweights physical examination relative to imaging and laboratory testing. The shift can produce errors when examination findings would have provided important information that imaging and laboratory testing miss.

Differential Diagnosis

Based on the history and examination, the clinician develops a differential diagnosis. The differential is the list of possible conditions that could explain the patient's presentation.

The breadth and accuracy of the differential affect subsequent evaluation. A differential that omits the actual condition leads to evaluation that does not address the actual cause. A differential that is too broad can lead to inefficient testing.

Diagnostic Testing

Based on the differential, the clinician selects diagnostic tests. The tests should help distinguish among the possibilities on the differential.

Test selection involves considerations of test characteristics, patient factors, costs, and various others. Inappropriate test selection can produce errors. The interpretation of test results requires expertise and depends on the clinical context.

For more on test selection, see How Doctors Choose the Right Diagnostic Test.

Clinical Reasoning

Clinical reasoning integrates the available information to reach a diagnosis. The reasoning involves consideration of the patterns suggested by history, examination, and test results, weighing the various possibilities, and arriving at the most likely diagnosis.

The quality of clinical reasoning is one of the most important determinants of diagnostic accuracy. Errors in reasoning, even when the underlying information is adequate, can produce diagnostic errors.

Communication and Action

The diagnosis is communicated to the patient and used to guide treatment. Effective communication ensures that the patient understands the diagnosis and the recommended approach.

Errors in communication can produce problems even when the diagnosis itself is correct. Findings noted but not effectively communicated can be missed in subsequent care.

Follow-up and Evolution

For many situations, the diagnostic process continues over time. The response to treatment, the evolution of symptoms, and various other factors provide additional information that may confirm or modify the original diagnosis.

The willingness to revisit diagnoses based on new information supports accurate diagnosis over time.

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Where Errors Occur

Errors can occur at any point in the diagnostic process. Understanding the specific locations supports approaches to prevention.

Errors in Initial Information Gathering

Errors at the initial information gathering stage include incomplete history taking, missed examination findings, and various other patterns. The errors at this stage limit the information available for subsequent reasoning.

Errors in Differential Diagnosis

Errors in developing the differential include omitting important possibilities and including incorrect ones. A differential that omits the actual condition cannot lead to correct diagnosis.

Errors in Test Selection

Errors in test selection include ordering inappropriate tests that do not address the relevant questions and not ordering tests that would have provided important information.

Errors in Test Interpretation

Errors in test interpretation include missing findings on imaging or laboratory studies, misinterpreting findings, and various other patterns.

For more on imaging interpretation specifically, see Can Medical Imaging Be Misinterpreted?.

Errors in Clinical Reasoning

Errors in clinical reasoning include the various cognitive biases that affect diagnostic thinking. These errors can produce incorrect diagnoses even when the underlying information is adequate.

Errors in Communication

Errors in communication include findings noted but not effectively communicated, miscommunication among providers, and various other patterns. These errors can produce problems even when other aspects of diagnosis are correct.

Errors in Follow-up

Errors in follow-up include failure to revisit diagnoses when subsequent information should have prompted reconsideration, and various other patterns.

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Cognitive Factors in Diagnostic Errors

Cognitive factors are among the most studied contributors to diagnostic errors. Several specific patterns are common.

Anchoring

Anchoring occurs when initial impressions about the diagnosis dominate subsequent thinking. The clinician forms an initial hypothesis and continues to interpret subsequent information in the context of that hypothesis, even when the new information does not support it.

The bias is particularly common when initial impressions are formed quickly based on limited information. The continued interpretation of evidence to support the initial hypothesis can produce errors when the initial hypothesis is incorrect.

Premature Closure

Premature closure occurs when evaluation stops before the actual cause is identified. The clinician reaches a conclusion before considering all reasonable possibilities, often because one possibility seems sufficient or because time pressure prevents more comprehensive consideration.

Availability Bias

Availability bias occurs when common conditions are considered more readily than uncommon ones, even when the patient's specific situation suggests an uncommon condition. The clinician's mental availability of certain diagnoses affects what is considered.

The bias can lead to assignment of common diagnoses when uncommon conditions are actually present.

Confirmation Bias

Confirmation bias occurs when evidence supporting an initial impression is given more weight than disconfirming evidence. The clinician may notice and remember findings that support the initial diagnosis while not adequately considering findings that argue against it.

Diagnosis Momentum

Diagnosis momentum occurs when a diagnosis, once made, persists despite subsequent evidence that should have prompted reconsideration. The continued treatment based on the original diagnosis can occur for extended periods even when the original diagnosis was incorrect.

Affective Bias

Affective bias occurs when feelings about the patient or the situation affect diagnostic reasoning. Patients who are particularly anxious, who have psychological diagnoses, who are difficult to interact with, or various other factors can produce diagnostic biases.

Search Satisfaction

Search satisfaction (sometimes called satisfaction of search) occurs when finding one abnormality reduces attention to others. After identifying a finding that explains some symptoms, the clinician may not adequately search for additional findings that would explain other aspects of the presentation.

Framing Effects

Framing effects occur when how information is presented affects how it is interpreted. The same information presented in different ways can lead to different diagnostic conclusions.

Overconfidence

Overconfidence in diagnosis can prevent recognition of uncertainty that should prompt additional evaluation. Clinicians sometimes feel more certain about diagnoses than the available information actually supports.

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System Factors in Diagnostic Errors

Beyond cognitive factors, system-level features of healthcare contribute to errors.

Time Pressure

Time pressure in clinical encounters affects diagnostic accuracy. Rushed encounters limit the time available for comprehensive history taking, examination, and reasoning.

The effects of time pressure are particularly pronounced for complex patients, atypical presentations, and various other situations requiring careful evaluation.

Workload

High clinician workload affects performance. The cumulative effect of seeing many patients can produce fatigue that affects subsequent encounters. The pressure to maintain throughput can affect how much attention each patient receives.

Care Fragmentation

Care fragmentation across multiple providers creates challenges. Patients seeing various specialists for different aspects of their care may not have any single provider who integrates the full picture. Important information may be missed because no single provider is responsible for the comprehensive view.

Communication Failures

Communication failures among providers contribute to errors. Findings noted by one provider may not reach another provider who needs them. Various other communication failures can prevent integration of information that would support correct diagnosis.

Information System Limitations

Limitations in information systems contribute to errors. Electronic health records, while supporting various functions, can also produce challenges including alert fatigue, copy-paste errors, and various other patterns. Important information may be buried in extensive records.

Inadequate Follow-up Systems

Systems for ensuring follow-up of test results and various other elements are sometimes inadequate. Findings that should have triggered specific actions may not be acted upon when systems do not support reliable follow-up.

Limited Specialty Access

Limited access to specialty expertise can contribute to errors. For patients who would benefit from specialty consultation, inability to access specialists can produce delays or errors.

Quality Improvement Limitations

Limitations in quality improvement processes can prevent identification and correction of recurrent error patterns. Without systematic measurement and intervention, errors continue to occur in patterns that could be addressed.

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Patient Factors in Diagnostic Errors

Patient factors also contribute to diagnostic errors.

Atypical Presentations

Atypical presentations of conditions are particularly likely to produce errors. The typical features that would lead to recognition may be absent. The clinician may consider various familiar diagnoses without recognizing the actual condition.

For more on atypical presentations, see Most Commonly Misdiagnosed Conditions.

Multiple Conditions

Patients with multiple medical conditions present diagnostic challenges. New symptoms can be attributed to existing conditions when they actually represent new problems. The integration of multiple conditions in diagnostic reasoning is challenging.

Communication Barriers

Communication barriers between patients and providers can affect diagnosis. Language barriers, cultural barriers, health literacy issues, and various other factors can prevent effective communication.

Patient Difficulty Articulating Symptoms

Some patients have difficulty articulating their symptoms accurately. The descriptions provided may not capture the actual experience adequately. Clinicians may rely on the descriptions provided without adequate exploration.

Patient Resistance to Specific Evaluations

Some patients resist specific evaluations. The resistance may be based on cost, fear of procedures, distrust of providers, or various other factors. The resistance can prevent evaluation that would support diagnosis.

Specific Patient Populations

Specific patient populations have particular challenges. Women experience misdiagnosis at higher rates than men for various conditions. Older adults' symptoms are sometimes attributed to aging. Patients with mental health diagnoses sometimes have medical symptoms attributed to mental health causes. Various other patterns affect specific populations.

Patient Factors That Increase Diagnostic Difficulty

Various patient factors increase diagnostic difficulty. Limited communication ability for any reason. Multiple medical comorbidities. Atypical presentations of common conditions. Rare conditions. Various other factors all contribute.

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Specific Patterns of Errors

Several specific patterns of errors are common in diagnostic medicine.

Conditions Mistaken for Other Conditions

Some misdiagnoses involve confusion among conditions with similar features. Heart attacks mistaken for indigestion or anxiety. Strokes mistaken for vertigo or migraine. Cancers mistaken for benign conditions. Various other specific confusions occur.

Failure to Diagnose

Failure to diagnose occurs when conditions present but are not identified. The patient does not receive a diagnosis for the actual condition, with consequent absence of appropriate treatment.

Delayed Diagnosis

Delayed diagnosis occurs when the correct diagnosis is eventually reached but only after significant delay. The delay allows the underlying condition to progress.

For more on this distinction, see Misdiagnosis vs Delayed Diagnosis: What's the Difference?.

Incomplete Diagnosis

Incomplete diagnosis occurs when one aspect of the diagnosis is correct but other important aspects are missed. A cancer might be correctly identified but its specific subtype or stage might be misidentified.

Errors in Imaging Interpretation

Errors in imaging interpretation include missed findings, misinterpreted findings, and various other patterns. Studies have found imaging error rates of approximately 3 to 5 percent in routine practice, with higher rates for specific challenging situations.

Errors in Laboratory Testing

Errors in laboratory testing can include sample issues, processing errors, interpretation errors, and various other patterns. The errors can affect downstream diagnosis.

Pathology Errors

Pathology errors include errors in initial interpretation, differences among pathologists in evaluating the same specimens, and various other patterns. Pathology second opinions sometimes change diagnoses.

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Specific Settings and Their Error Patterns

Different healthcare settings have somewhat different patterns of errors.

Primary Care

Primary care settings handle wide ranges of conditions with limited time per encounter. The challenge of recognizing serious conditions among many common ones can produce both misdiagnosis and delayed diagnosis.

The strengths of primary care including continuity over time can support recognition of conditions that emerge gradually. The limitations including time pressure and breadth of conditions can produce errors.

Emergency Departments

Emergency departments face specific challenges including high volume, urgency, limited information about patients, and the need to identify time-critical conditions quickly. Studies of emergency department diagnostic accuracy have found error rates ranging from 5 to 15 percent for various conditions.

For specific conditions including heart attacks, strokes, pulmonary embolism, and various others, emergency departments face particular challenges in atypical presentations.

Specialist Care

Specialist care typically focuses on conditions within the specialist's area. Errors tend to involve recognition of conditions within or adjacent to the specialty. For conditions affecting multiple specialties, the integration of care can produce challenges.

Outpatient Settings

Outpatient settings face challenges of follow-up and continuity. Symptoms developing between visits, new findings on tests not adequately followed up, and various other elements contribute to errors.

Inpatient Settings

Inpatient settings involve intensive evaluation but face complexity of acutely ill patients with multiple conditions. The integration of various findings can be challenging.

After-Hours Care

After-hours care, including overnight emergency interpretation and various other situations, may have somewhat different error patterns than daytime care. The specific patterns vary among institutions.

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How Errors Compound

Errors at one stage of the diagnostic process can compound through subsequent stages.

Initial Errors Affecting Subsequent Evaluation

Errors in initial information gathering or differential diagnosis affect subsequent evaluation. Tests selected based on incorrect differentials may not address the actual cause. Reasoning based on incomplete information may reach incorrect conclusions.

Errors Affecting Treatment Response

Errors leading to incorrect diagnoses affect treatment response. Treatment based on incorrect diagnoses does not address the actual cause, with the failure of treatment sometimes appropriately prompting reconsideration but sometimes leading to assumption of treatment-resistant disease.

Errors Affecting Patient Engagement

Errors affecting patient engagement can produce additional problems. Patients whose concerns have been dismissed may not return for evaluation when symptoms persist or evolve. The disengagement can prevent identification of conditions that should have been recognized.

Errors Affecting Provider Reasoning

Errors that have been documented in records can affect subsequent provider reasoning. Other providers may anchor on the documented diagnosis without independently evaluating the situation. The original error can persist through subsequent encounters.

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What Reduces Errors

Several specific approaches reduce diagnostic errors.

Systematic Approaches

Systematic approaches to evaluation reduce errors. Structured history taking, standardized examination, systematic differential diagnosis, and various other elements support comprehensive evaluation.

Specialty Expertise When Appropriate

Specialty expertise when relevant supports better diagnosis than general expertise alone. Subspecialty radiologists, pathologists, and clinicians with concentrated experience in specific conditions often provide insights that more general evaluation cannot match.

Decision Support Systems

Computer-based decision support systems support diagnostic accuracy by suggesting possibilities the clinician may not have considered, providing reminders about specific testing for various situations, and supporting various other aspects of diagnosis.

Artificial Intelligence

AI applications in diagnosis are evolving rapidly. The technology supports detection of subtle findings, identification of patterns, and various other aspects of diagnosis. The combination of AI support with expert human judgment often produces better outcomes than either approach alone.

Standardized Protocols

Standardized diagnostic protocols for specific situations support consistency. The protocols address common situations and various specific challenging ones, supporting more reliable evaluation.

Quality Improvement Initiatives

Systematic quality improvement initiatives address errors over time. Peer review, monitoring of error rates, and targeted interventions for specific patterns all contribute.

Patient Engagement

Active patient engagement supports better diagnosis. Patients who provide comprehensive history, communicate concerns clearly, persist when warranted, and various other elements contribute to better diagnostic outcomes.

Communication Improvements

Improvements in communication among providers and with patients reduce errors. Electronic systems, structured handoffs, and various other innovations contribute.

Education and Training

Ongoing education and training, including specific training on cognitive biases and various other diagnostic challenges, support improved performance.

Second Opinions

Second opinions for significant decisions provide additional perspectives that can identify aspects missed in initial evaluation.

For more on this, see What Is a Medical Second Opinion and Why It Matters.

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What Patients Can Do

For individual patients, several specific approaches can reduce risk of diagnostic errors.

Provide Comprehensive History

Comprehensive history is one of the most important patient contributions to accurate diagnosis. Specific descriptions of symptoms with timing, character, and patterns; comprehensive medical history; family history; medications; and various other elements all contribute.

Communicate Concerns Clearly

Clear communication of concerns supports productive evaluation. Specific descriptions of what is concerning support better engagement.

Persist When Warranted

Persistence in seeking evaluation when symptoms continue despite initial reassurance supports eventual identification of conditions that may have been missed.

The patient's intuition that something is wrong often reflects accurate recognition.

Pursue Specialty Consultation When Appropriate

For specific situations where specialty expertise is appropriate, consultation with relevant specialists supports better diagnosis than primary care evaluation alone.

Consider Second Opinions

For significant decisions, second opinions provide additional perspectives. The investment in second opinions is often worthwhile.

Engage Patient Advocacy Resources

Patient advocacy organizations for specific conditions provide expertise and support. These resources can identify specialists, provide information about specific conditions, and support various other aspects of seeking accurate diagnosis.

Maintain Records

Comprehensive personal medical records support continuity of care and accurate evaluation.

Question When Things Do Not Make Sense

When aspects of the diagnostic process or the resulting diagnosis do not make sense, asking questions and seeking clarification supports accurate diagnosis. The questions may reveal aspects that need clarification or may identify issues warranting additional evaluation.

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Specific Approaches to Reducing Errors

Several specific approaches address aspects of diagnostic errors.

Diagnostic Time-Outs

Diagnostic time-outs involve pausing during the diagnostic process to reconsider whether the current direction is correct. The pause allows reconsideration of alternatives that may have been dismissed prematurely.

Differential Diagnosis Documentation

Documenting the differential diagnosis explicitly supports comprehensive consideration of possibilities. The documentation serves as a record that can be reviewed later if the initial direction does not produce expected results.

Forced Reasoning

Forced reasoning approaches require explicit consideration of specific alternatives. The structured approach prevents premature closure and supports comprehensive evaluation.

Diagnostic Calibration

Diagnostic calibration involves checking the level of confidence in diagnoses against the actual accuracy. The exercise helps clinicians develop more accurate sense of when their diagnoses are likely to be correct.

Peer Review

Peer review processes support identification of error patterns. Random review of diagnoses and review of specific cases with concerning features both contribute.

Patient Feedback Systems

Patient feedback about whether diagnoses turned out to be correct supports learning. Systematic collection of this information identifies patterns that can inform improvement.

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Common Misconceptions About Diagnostic Errors

Several misconceptions about diagnostic errors deserve attention.

The idea that errors only occur with poor providers is overstated. Errors occur across the full range of providers and settings, though rates may vary.

The idea that errors are usually due to negligence is misleading. Most errors involve complex combinations of factors rather than simple negligence.

The idea that more testing eliminates errors is overstated. Excessive testing can produce its own problems including false positives. The appropriate balance of testing matches the clinical situation.

The idea that artificial intelligence will eliminate errors is also overstated. AI provides specific support but does not eliminate the need for expert judgment. The combination of AI and human expertise typically performs better than either alone.

The idea that errors are inevitable and cannot be reduced is misleading. Various interventions have demonstrably reduced error rates over time. The trajectory continues to favor reduced errors.

The idea that the patient is at fault when errors occur is generally not accurate. While patient communication matters, the responsibility for diagnosis rests primarily with clinicians.

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When to Be Concerned About Possible Errors

Several specific situations should prompt concern about possible diagnostic errors.

Treatment that is not working despite appropriate use suggests possible errors.

Symptoms that worsen despite treatment, particularly when the diagnosis would predict improvement, warrant attention.

New symptoms inconsistent with the diagnosis suggest possible errors.

Test results that do not fit the diagnosis warrant attention.

Persistent concerns about the situation despite reassurance deserve respect.

Time-critical conditions that were not adequately considered may warrant evaluation.

For more on this, see When Should You Suspect a Wrong Diagnosis?.

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When to See a Specialist

For evaluation of medical concerns where errors may have occurred, several types of specialists may be involved.

Primary care providers can address most initial concerns and refer to specialists when appropriate.

For specific symptom patterns suggesting specific specialty conditions, appropriate specialists provide focused expertise.

For complex or unusual situations, evaluation at academic medical centers or specialized institutions may provide expertise that more general evaluation cannot match.

For rare or undiagnosed conditions, specialized programs at major medical centers focus on these challenging situations.

For situations involving substantial concerns about prior diagnostic errors, evaluation at specialized centers may help.

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Conclusion

Diagnostic errors arise from complex combinations of factors involving the inherent difficulty of diagnosis, characteristics of human cognition, system-level features of healthcare delivery, and various other elements. Understanding how errors happen supports approaches to reducing them.

The diagnostic process is a structured sequence including initial information gathering, differential diagnosis, testing, clinical reasoning, communication, and follow-up. Errors can occur at any point, with the cumulative effect determining whether the final diagnosis is correct.

Cognitive factors contributing to errors include anchoring, premature closure, availability bias, confirmation bias, diagnosis momentum, and various others. System factors include time pressure, workload, care fragmentation, communication failures, and various others. Patient factors include atypical presentations, multiple conditions, communication barriers, and various others. Each category of factors contributes to overall error rates.

Approaches to reducing errors include systematic approaches to evaluation, specialty expertise when appropriate, decision support systems, AI applications, standardized protocols, quality improvement initiatives, patient engagement, communication improvements, education and training, and second opinions for significant decisions.

For individual patients, several approaches reduce risk of being affected by diagnostic errors. Providing comprehensive history, communicating concerns clearly, persisting when warranted, pursuing specialty consultation when appropriate, considering second opinions for significant decisions, engaging patient advocacy resources, maintaining records, and questioning when things do not make sense all contribute.

The encouraging element of this picture is that the trajectory continues to favor patients. Diagnostic accuracy has improved over recent decades and continues to improve. The combination of better technology, better processes, and more engaged patients produces gradually better outcomes over time.

For most patients, the practical message is that engagement with one's own healthcare, including appropriate vigilance about diagnostic accuracy, supports the best outcomes. The combination of trust in the diagnostic process with awareness of potential issues produces a balance that contributes to good care.

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Medical Disclaimer

This content is for informational purposes only and does not constitute medical advice. Individuals should consult a qualified healthcare provider for diagnosis and treatment.