Human beings, in all lines of work, make errors. Errors can be prevented by designing systems that make it hard for people to do the wrong thing and easy for people to do the right thing.

Institute of Medicine,* 1999
To Err Is Human: Building a Safer Health System

* The Institute of Medicine (IOM) is now called the National Academy of Medicine.

It is estimated that as many as 98,000 people die in any given year from medical errors that occur in hospitals. A significant number of those deaths is due to medication errors. That number is greater than deaths from motor vehicle accidents, breast cancer, or AIDS—three causes that receive far more public attention. Indeed, more people die annually from medication errors than from workplace injuries. Add the financial cost to the human tragedy, and medical error easily rises to the top ranks of urgent, widespread public problems (NCCMERP, 2026).

Medical errors are often preventable, yet they continue to affect millions of lives, undermine public trust, and impose a heavy burden on health systems worldwide. Despite increasing visibility, medical errors remain a complex and under-addressed phenomenon, especially when considering their broader impact beyond the individual level (Sarquis Rivera et al., 2026).

Along with being among the leading causes of death across all age groups in the United States, medical errors can result in long-term morbidity and disability. This translates into prolonged hospital stays and additional treatments, further increasing risks for secondary conditions and creating complex clinical scenarios (Sanchez and Corvalan, 2025).

Years after the Institute of Medicine's renowned report, “To Err is Human,” which for the first time addressed the importance of medical errors, there are still serious concerns about patient safety. Similar mistakes occur in different settings and unknowingly patients continue to be affected by the adverse outcomes of preventable errors (Aghighi et al., 2024).

From an economic perspective, medical errors significantly impact the public perception of healthcare systems, eroding patient trust and reducing the likelihood of seeking necessary medical care. They can cause irreparable damage to the professional reputation of healthcare providers and institutions, who must bear costs associated with additional treatments and legal compensations, alongside indirect costs such as decreased productivity and personnel burnout (Sanchez and Corvalan, 2025).

Direct costs include expenses related to treating complications and adverse events, as well as medical malpractice compensation. Indirect costs, including lost productivity and broader social costs, are equally significant. Medical errors represent a complex, multifactorial problem affecting patients, healthcare professionals, and healthcare systems worldwide, with public health and economic implications that underscore the urgent need for effective intervention (Sanchez and Corvalan, 2025).

1.1 Medical Errors

A medical error is an act of omission or commission in planning or execution that contributes to, or has the potential to contribute to, an unintended outcome. It is a failure in the healthcare delivery process—whether or not it actually hurts the patient. A medical error is a deviation from standard care. For example:

• A nurse misreads a medication label and administers the wrong dose.
• A physician fails to follow up on a critical lab result.
• A surgeon makes an incorrect incision.

Medical errors can produce wide-ranging consequences, from minor and temporary to severe and permanent. According to severity, medical errors can be classified as (Sanchez and Corvalan, 2025):

• Mild adverse events: Errors causing minimal or temporary harm, such as mild allergic reactions to medications or minor injection site infections.
• Moderate adverse events: Errors causing significant but reversible harm, such as bone fractures from hospital falls or adverse medication reactions requiring hospitalization.
• Severe adverse events: Errors causing permanent or life-threatening harm, such as brain injuries during surgery or severe allergic reactions with anaphylactic shock.
• Fatal adverse events: Errors resulting in patient death, such as fatal medication errors or serious nosocomial infections.
• Near-miss events: Adverse events that occurred due to errors but caused no actual harm.

1.2 Sentinel Events

In 1996, The Joint Commission adopted the Sentinel Event Policy to support hospitals in investigating and analyzing severe patient safety incidents. Sentinel events are defined as patient-safety events that result in death, permanent harm, or severe temporary harm. Sentinel events serve as warning signals of potential systemic issues that could lead to future harm if unaddressed. The policy supports healthcare organizations through in-depth systemic evaluations (Liepelt and Kirchhoff, 2025).

A sentinel event is a subcategory of medical errors and adverse events as specifically defined by The Joint Commission. It is an unexpected occurrence involving death, permanent harm, or severe temporary harm. The word sentinel is used because these events signal the need for immediate investigation and response to prevent them from ever happening again.

Under the Sentinel Event Policy, healthcare organizations must have a policy detailing how the organization addresses sentinel events; they are encouraged to report voluntarily any event that meets this definition, regardless of whether it is specifically listed in the Sentinel Events Policy (JC/NQF, 2026, May).

Sentinel events focus on the severity of the outcome (or a high-risk near-miss that signals a critical system weakness). For example:

• an inpatient suicide
• an infant abduction
• surgery performed on the wrong patient or wrong body part (often called a "Never Event")
• a medication error that leads directly to patient death

The outcome is always catastrophic or extremely high-risk. All sentinel events caused by care delivery failures are medical errors.

The most common sentinel events are (Joint Commission, 2025):

• patient falls (49%)
• wrong surgery (8%)
• delay in treatment (8%)
• patient suicide/death by self-inflicted injurious behavior (8%)
• unintended retention of foreign objects (8%)
• healthcare workplace violence-related events (4%)

1.3 Serious Reportable Events

A Serious Reportable Event (SRE) bridges the gap between a medical error and a sentinel event. Commonly known as a “Never Event,” the term SRE was coined by the National Quality Forum (NQF) to describe a specific list of non-negotiable, largely preventable adverse events that should simply never happen if proper safety protocols are followed.

Serious Reportable Events are patient safety events deemed serious, harmful, preventable, and therefore indicative of vulnerabilities in a healthcare setting’s safety systems. Since 2002, the purpose of the National Quality Forum’s SRE List has included facilitating consistent reporting, driving national improvement via shared learning, and preventing the recurrence of these events. By assessing the underlying causes of these events, healthcare organizations can identify causative factors and bolster their quality improvement efforts (NQF, 2026, January).

To qualify as an SRE, an event must be serious and largely preventable. Serious means an event results in death or contributes to physical, emotional, or psychological patient harm. A serious event requires a major intervention such as surgery, a higher level of care, or treatment post discharge, or impairs a patient’s ability to perform activities of daily living(NQF, 2026, January).

Largely preventable means an event that is likely avoidable by means currently available within the generally accepted performance standards of care. A largely preventable event triggers further investigation into causative factors (NQF, 2026, January).

1.4 Comparison Cross-Over

In healthcare, the terms medical error and sentinel event are closely related, but they are not the same thing. The easiest way to think about the difference is that one describes a mistake, while the other describes a catastrophic outcome.

An event can be both a Serious Reportable Event and a Sentinel Event. For example, if a surgeon operates on the wrong leg, it is an SRE (it is on the NQF's explicit list) and it is a Sentinel Event (it causes severe, permanent harm).

An SRE might not be a Sentinel Event. For example, if an infant is discharged to the wrong family but the mistake is realized and corrected the next day without permanent psychological or physical harm, it is still an SRE (infant discharge to the wrong person is on the NQF list), but it may not meet The Joint Commission's threshold for a sentinel event if no permanent harm occurred.

A Sentinel Event might not be an SRE. For example, if a patient commits suicide within 72 hours of discharge from an inpatient behavioral health unit, The Joint Commission considers this a sentinel event requiring an immediate investigation. However, because it happened post discharge, it may not fit the strict criteria of the NQF’s healthcare-facility SRE list.