What Is a Diagnostic Error in Health Care and Why It Matters

Every day, millions of people rely on medical professionals to identify and treat their health problems. While modern medicine has made incredible advances, diagnostic errors remain a major concern in patient safety. These errors can lead to delayed treatment, unnecessary procedures, or worse: harm that could have been avoided.

In this article, we’ll explore what diagnostic errors are, why they happen, how they’re defined and measured, and what can be done to prevent them. Whether you’re a patient, doctor, or healthcare professional, understanding diagnostic errors is essential to improving health outcomes and restoring trust in the healthcare system.

What Is a Diagnostic Error?

At its core, a diagnostic error happens when there is a failure to provide an accurate and timely explanation of a patient’s health problem or a failure to communicate that explanation effectively. It can take several forms:

• A missed diagnosis, where the condition is never identified
• A wrong diagnosis, where the incorrect condition is identified
• A delayed diagnosis, where the correct condition is found too late

Importantly, a diagnosis isn’t just about naming a disease. It’s also about making sure that the information reaches the patient in a way they understand. Without communication, even an accurate diagnosis is incomplete.

Why Do Diagnostic Errors Happen?

Diagnostic errors are rarely caused by a single issue. Instead, they often result from a combination of cognitive mistakes, system failures, and patient factors.

For example, a clinician may misinterpret test results due to lack of experience. Or the healthcare system might fail to schedule necessary follow-ups due to communication breakdowns. In some cases, patients may provide incomplete or misleading information, which complicates the diagnostic process.

Experts categorize the causes of diagnostic errors into three types:

1. Cognitive errors – such as flawed reasoning, knowledge gaps, or misjudgments
2. System-related errors – including poor coordination, technical failures, or limited access to care
3. No-fault errors – when unusual presentations or rare diseases make diagnosis especially difficult

These errors often overlap. For instance, a poorly designed system might increase the risk of cognitive errors, especially in high-stress clinical environments.

How Diagnostic Errors Affect Patients

The consequences of diagnostic errors vary widely. In some cases, they may cause no harm. But in others, they can lead to serious physical, emotional, and financial damage. A misdiagnosed cancer, for example, could delay life-saving treatment. A mistaken diagnosis might result in unnecessary surgery or toxic medication. Even if the patient recovers, the emotional toll can last for years.

Moreover, these errors can shake public trust in the healthcare system. They also increase costs by triggering unnecessary treatments, lawsuits, and repeat testing.

The Role of Communication in Diagnosis

Accurate diagnosis is only part of the equation. Timely and clear communication is just as vital. If a doctor identifies a serious condition but fails to inform the patient or does so in language the patient doesn’t understand the outcome can still be harmful.

The definition of diagnostic error now reflects this: a diagnosis must not only be correct and timely, it must also be effectively communicated. This is especially important in emergency cases, or when dealing with vulnerable populations like children, elderly patients, or individuals with limited health literacy.

Can Diagnostic Errors Be Prevented?

While not all errors can be avoided, many diagnostic mistakes are preventable. The key lies in improving both the process of diagnosis and the systems that support it.

Here’s how healthcare teams can reduce risk:

• Encourage collaboration and second opinions, especially for complex cases
• Use structured diagnostic tools and decision support systems
• Foster a culture where doctors feel safe acknowledging uncertainty
• Ensure patients are active participants in their care, by sharing full histories and asking questions
• Improve communication and hand-offs between providers
• Train clinicians in critical thinking and cognitive bias awareness

Importantly, healthcare organizations must treat diagnostic errors and near misses as learning opportunities, not failures to be hidden.

Understanding Overdiagnosis and Overuse

Another challenge in modern medicine is overdiagnosis, when a condition is correctly identified, but it would never have caused harm if left undetected. This can lead to overtreatment, which brings its own risks and costs.

Overdiagnosis isn’t the same as a diagnostic error, but it is closely related. It often results from increased testing, broader disease definitions, and fear of missing a diagnosis. Reducing unnecessary testing is a key part of improving diagnostic quality.

Why Measuring Diagnostic Errors Is Difficult

Unlike other medical mistakes, diagnostic errors are hard to track. They can occur at any stage, from the first appointment to final follow-up and sometimes aren’t recognized until much later.

Several models exist for understanding and measuring these errors. Some focus on missed opportunities, while others look at failures in the diagnostic process itself. Still, most experts agree that better data collection, case reviews, and patient feedback are needed to improve how errors are monitored and prevented.

The Institute of Medicine outlines five goals for measuring diagnostic error:

1. Identify how often errors happen
2. Understand their causes and risks
3. Evaluate prevention strategies
4. Support medical education
5. Ensure accountability

Final Thoughts

Diagnostic errors represent one of the most complex and costly challenges in healthcare today. They stem from a mix of system flaws, human limitations, and communication gaps. But they’re not inevitable. With the right tools, teamwork, and transparency, healthcare providers can dramatically reduce the risk of misdiagnosis and improve patient outcomes.

By understanding what diagnostic errors are, how they occur, and what can be done to prevent them, we take a vital step toward safer, smarter, and more patient-centered care.