What are the three different categories of medical errors?

September 23, 2025 •

4 min read

Reports indicate medical errors are a significant public health problem, potentially ranking among the leading causes of death. Understanding what are the three different categories of medical errors? is the first step toward promoting safer healthcare environments and becoming a more informed patient advocate.

Quick Summary

The three primary categories of medical errors are diagnostic, treatment, and communication errors, each stemming from complex systemic issues and human factors rather than just individual fault. By understanding these classifications, we can better identify risks and implement strategies to improve patient safety and healthcare quality.

Key Points

Diagnostic Errors: Involve misdiagnosis, delayed diagnosis, or missed diagnosis, often linked to cognitive biases, time pressure, or systemic issues.
Treatment Errors: Comprise mistakes made during a procedure, including medication errors (wrong dose, wrong drug) and surgical errors (wrong site, retained instruments).
Communication Errors: Stem from poor information transfer between staff or with patients, such as during handoffs or discharge instructions.
Systemic Nature: Medical errors are frequently the result of systemic weaknesses and human factors like fatigue, staffing issues, and technology design, not just individual incompetence.
Patient Safety Initiatives: Many preventable medical errors can be reduced by adopting a systems-based approach, using tools like checklists and focusing on root cause analysis.
Active Participation: Patients can play a vital role in preventing errors by being informed, asking questions about their care, and verifying information with their healthcare team.

Medical errors are a deeply complex issue within the healthcare system, impacting countless patients each year. They are not merely isolated incidents caused by individual negligence, but often the result of complex systemic failures, human factors, and communication breakdowns within a high-stakes environment. By categorizing these errors, patient safety advocates and healthcare professionals can better identify the root causes and implement targeted interventions to prevent future harm.

The Three Primary Categories of Medical Errors

1. Diagnostic Errors

Diagnostic errors occur when there is a failure to establish an accurate and timely explanation of a patient's health problem, or to communicate that information effectively. This category is recognized as one of the most harmful types of medical errors, with common issues including misdiagnosis, delayed diagnosis, or a completely missed diagnosis. These errors can have severe consequences, leading to delayed or incorrect treatment. The contributing factors are often multifaceted, including:

Cognitive Biases: Mental shortcuts, such as 'anchoring bias' where a clinician fixates on an initial diagnosis despite new evidence, or 'confirmation bias,' where they only seek information that supports their initial hypothesis.
Systemic Issues: Inadequate diagnostic technology, a heavy workload, and time pressure can hinder a clinician's ability to conduct a thorough evaluation.
Patient Factors: A patient's inability to accurately convey their medical history or follow up on test results can also contribute to a diagnostic error.

2. Treatment Errors

Treatment errors are a broad category that covers mistakes made during the administration of a treatment or procedure. These mistakes involve the use of a wrong plan or a failure to complete a planned action as intended. This category can be further broken down into several sub-types, which often have devastating results for patients. Contributing factors range from lack of training and fatigue to poorly designed equipment.

Medication Errors

Medication errors are a highly reported type of treatment error and can occur at any stage, from prescribing to dispensing to administration. They are a serious concern, affecting millions annually. Examples include:

Prescribing Errors: Writing the wrong medication, incorrect dose, or a drug interaction not accounted for.
Dispensing Errors: A pharmacist providing the wrong medication or an incorrect dosage amount.
Administration Errors: Giving the wrong patient medication, using the wrong route, or administering at the wrong time.

Surgical Errors

Often referred to as 'never events' because they are considered preventable and should never occur, surgical errors are a critical part of the treatment error category. Examples include:

Wrong-site surgery: Operating on the wrong part of the body, such as the wrong leg or wrong side of the brain.
Wrong-procedure surgery: Performing the wrong type of surgery on a patient.
Retained surgical items: Leaving instruments, sponges, or other items inside a patient's body post-surgery.

3. Communication Errors

Communication failures are a prevalent and significant cause of medical errors, often bridging the gap between diagnosis and treatment. Ineffective communication can lead to devastating consequences and is often a symptom of systemic issues within healthcare. Some of the most common communication failures include:

Poor Patient Handoffs: Miscommunication or failure to relay crucial information about a patient during shift changes.
Communication with Patients: Failure to effectively communicate a diagnosis, treatment plan, or discharge instructions, leading to patient non-compliance or confusion.
Inaccurate Record Keeping: Illegible handwriting or errors in electronic health records (EHRs) can be transcribed incorrectly, leading to errors downstream.

Comparing the Three Categories of Medical Errors

To better understand the distinctions, a comparison table can be useful.


Category	Definition	Common Examples	Underlying Causes	Potential Impact
Diagnostic	Failure to provide a correct and timely diagnosis.	Misdiagnosis, delayed diagnosis, missed diagnosis.	Cognitive biases, system limitations, time constraints.	Worsened health condition, unnecessary treatment, fatal outcome.
Treatment	Failure to administer a treatment or procedure as intended.	Medication errors (wrong dose), surgical errors (wrong site), anesthesia errors.	Inadequate training, fatigue, technology issues, communication breakdowns.	Injury, infection, loss of function, death.
Communication	Breakdowns in transferring information between healthcare providers or with patients.	Poor patient handoffs, incomplete patient education, illegible notes.	Systemic culture, language barriers, disruptive environment.	Treatment delays, inappropriate care, repeat testing.

The Role of Systemic Issues and Human Factors

The Swiss Cheese Model of accident causation, popularized by James Reason, effectively explains how medical errors occur when multiple layers of defense fail. A single error rarely leads to harm; instead, a series of latent system flaws (e.g., inadequate staffing, poor training) align with an active human error (e.g., a mistake by a tired nurse) to cause an adverse event. This perspective shifts the focus from blaming individuals to fixing the flawed systems that enable mistakes to happen. Organizations like the Agency for Healthcare Research and Quality (AHRQ) emphasize understanding and addressing these complex systemic causes to improve patient safety, with resources and data available on their website [psnet.ahrq.gov].

Conclusion: Promoting a Culture of Patient Safety

Recognizing the distinction between the three main categories of medical errors—diagnostic, treatment, and communication—is foundational for any initiative aimed at improving patient safety. By moving beyond a culture of individual blame and adopting a systems-based approach, healthcare institutions can better address the root causes of errors, such as fatigue, communication failures, and technology design flaws. This approach, which includes implementing tools like checklists and standardized protocols, is the most effective path forward for reducing preventable harm and ensuring that every patient receives the safe, high-quality care they deserve.

Frequently Asked Questions

Diagnostic errors occur when there is a failure to establish an accurate and timely explanation of a patient's health problem. This can include a misdiagnosis, a delayed diagnosis, or a missed diagnosis entirely, leading to inappropriate or deferred treatment.

Common examples include medication errors, such as giving the wrong drug or dose; surgical errors, like operating on the wrong body part; and applying an inappropriate or unintended therapy during a procedure.

Breakdowns in communication can lead to errors by causing misinterpretations of orders, failure to relay critical patient information during shift changes, or insufficient instruction provided to the patient about their care.

While human factors play a role, most medical errors are the result of complex systemic failures. These can include issues with protocols, inadequate staffing, fatigue, or technology design, which create an environment where mistakes are more likely to occur.

A 'never event' is a preventable and serious medical error that should never happen in healthcare. Examples of surgical never events include operating on the wrong body part or leaving a surgical instrument inside a patient.

While EHRs are designed to improve safety, they can introduce new types of errors due to poor design, confusing user interfaces, or contributing to cognitive overload for clinicians. Mistakes can occur with incorrect data entry or when systems fail to communicate accurately.

Patients can be active participants in their safety by asking questions about their care, ensuring their medical history and allergies are accurately recorded, and verifying procedures or medications with their healthcare providers.