Medical errors are rarely the fault of a single “bad apple” clinician. Instead, they are almost always the result of multiple system weaknesses aligning at the wrong moment. Nevertheless, human factors and individual vulnerabilities heavily influence safety. For example:

• Fatigue, sleep deprivation, extended shifts, and night shifts significantly degrade clinical decision-making, reaction times, and situational awareness.
• Cognitive overload and interruptions, such as a nurse being interrupted mid-way through a medication administration sequence, is far more likely to cause a missed safety check.
• Inexperience, lack of training, complex equipment, specialized electronic health record workflows, or a lack of familiarity with specific clinical protocols creates a high-risk environment for newer staff.

Errors can occur at any point throughout the patient care process. The most prevalent types include diagnostic errors, treatment errors, prevention errors, and communication errors (Sanchez and Corvalan, 2025).

2.1 Diagnostic Errors

A diagnostic error is defined as the failure to establish an accurate and timely explanation of the patient's health problem or failure to communicate that explanation to the patient. Diagnostic errors rarely happen due to simple incompetence. Instead, they stem from a mix of cognitive biases (how clinicians think) and systemic flaws (how healthcare environments operate).

Diagnostic errors are a grossly under-assessed patient safety and quality-of-care threat. Annual estimates of diagnostic error vary widely, from 40,000 to 4 million cases nationwide. Over half are related to cardiovascular events, infections, and cancers, and over 6% of these result in serious harm to patients (Hunter et al., 2024).

Diagnostic errors include:

• delayed diagnosis
• wrong diagnosis
• missed diagnosis

Diagnostic errors also include overdiagnosis, which can lead to unnecessary and potentially harmful treatments.

Diagnostic errors, such as misdiagnoses, unaddressed abnormal test results, delays in care or response, and missed diagnoses, can result in death or severe permanent patient harm. Delays in treatment increased by 56% between 2023 and 2024, with patient death reported as the most common outcome (Patel and Goldin, 2026).

The top five most misdiagnosed medical conditions in outpatient primary care clinical practice are pneumonia (6.7%), decompensated congestive heart failure (5.7%), acute renal failure (5.3%), cancer (5.3%), and urinary tract infection or pyelonephritis (4.8%). Alternatively, hospitalized patients show higher rates of missed vascular events (pulmonary embolism and myocardial infarction) and opportunistic infections (Patel and Goldin, 2026).

Over the past two decades, research has consistently shown that diagnostic errors are a significant concern in every healthcare setting. Epidemiologic studies show that diagnostic errors nearly always have multifaceted causes and arise from an interplay of contributing factors, including issues related to cognitive reasoning (inadequate data gathering, data interpretation, or clinical assessment), patient factors, and communication. Rates of diagnostic errors in acute care, ambulatory care, and emergency care remain unacceptably high (Khan et al., 2025).

2.2 Treatment Errors

Treatment errors occur after a diagnosis has been established. They are mistakes that happen during the administration of a chosen therapy, the performance of a surgical or clinical procedure, or the ongoing management of a patient's care. Unlike diagnostic errors, which are heavily rooted in cognitive reasoning, treatment errors are highly procedural and frequently linked to operational bottlenecks, system design flaws, and communication gaps.

Treatment errors span every phase of patient care, but they are most commonly concentrated in four specific areas: medication errors, surgical and procedural errors, equipment and technology failures, and monitoring and delay failures.

2.2.1 Medication Errors

Medication errors are a type of treatment error that can occur during prescribing, dispensing, or administration of medications. National Coordinating Council for Medication Error Reporting and Prevention defines a medication error as follows (NCCMERP, 2026):

“Any preventable event that may cause or lead to inappropriate medication use or patient harm while the medication is in the control of the healthcare professional, patient, or consumer. Such events may be related to professional practice, healthcare products, procedures, and systems, including prescribing, order communication, product labeling, packaging, and nomenclature, compounding, dispensing, distribution, administration, education, monitoring, and use.”

The misuse of therapeutic agents can lead to adverse drug events (ADEs) ranging from minor discomfort to life-threatening complications. Adverse drug events are broadly defined as injuries resulting from medical interventions related to drugs, including medication errors, adverse drug reactions, allergic responses, and overdoses. ADEs impose a significant burden on healthcare systems, with wide-ranging implications for patient safety, clinical outcomes, and resource utilization.

In the United States, ADEs contribute to approximately two million hospital admissions annually, resulting in extended lengths of stay and substantially increased healthcare expenditures. Additionally, ADEs account for approximately one million emergency department visits and 3.5 million physician office consultations each year, representing a significant strain on healthcare resources and capacity (Ye and Bronstein, 2025).

Look-alike/sound-alike (LASA) issues represent one of the most persistent hurdles in clinical documentation and pharmacy safety. When abbreviations look identical in hasty handwriting or sound nearly indistinguishable during a verbal or telephone order, the consequences can be immediate. The most common and problematic LASA abbreviations, acronyms, and shorthand symbols are broken down below.

Examples of Look-Alike, Sound-Alike, and Error Prone Abbreviations

• IU (International Unit) can be confused with IV (intravenous)
• Trailing zero (.5 mg) can be confused with 5 mg
• Misleading shorthand such as BID, TID, PO
• OD (right eye) can be confused with overdose
• QD (every day) can be confused with QOD (every other day)
• MS (morphine sulfate) can be confused with magnesium sulfate
• KCL (potassium chloride) can be confused with HCL (hydrochloride)
• Mg (milligram) can be confused with mcg (microgram)

In almost all cases, these types of orders should be written out with words.

Prescribing errors are a significant contributor to ADEs, occurring at multiple stages, including prescribing, transcription, dispensing, and administration. Common prescribing errors include inappropriate medication selection, incorrect dosing calculations, and failure to consider patient-specific factors such as renal or hepatic function, age-related physiologic changes, and concurrent medications. A study found that nearly 94% of hospitalized patients experienced at least one prescribing error during their admission, underscoring the pervasive nature of this problem (Ye and Bronstein, 2025).

Medication administration errors constitute another major cause of adverse drug events, occurring when incorrect medications are administered, correct medications are given in wrong doses or via inappropriate routes, or medications are administered at incorrect times. Contributing factors include clinical interruptions during medication preparation and administration, similar packaging or labeling of different pharmaceutical products, and increasingly complex medication regimens that challenge a healthcare provider’s cognitive capacity and attention to detail (Ye and Bronstein, 2025).

For healthcare providers, polypharmacy (>5 medications) should be a trigger for a thorough therapeutic review. Every patient’s medication regimen should be reviewed during each visit and coordinated with the patient’s other providers (NCCMERP, 2026).

Providers should make sure that each prescribed medication has a matching diagnosis and fits within the treatment plan. A patient-centered approach to medication management assures that medications are appropriate, safe, affordable, and easy to use. It also considers a patient’s ability and willingness to adhere to the medication plan (NCCMERP, 2026).

When a medication is added, the risks and benefits should be evaluated in context with other medications the patient is taking. Using standardized tools, such as the Beers Criteria* and STOPP/START Criteria** for use with older adults, allows a healthcare provider to screen patients carefully for potentially inappropriate medications (NCCMERP, 2026).

*Beers Criteria: Maintained by the American Geriatric Society, it catalogs medications that should generally be avoided or used with extreme caution in older populations.

**Stopp/Start Criteria: (Screening Tool of Older Persons’ Prescriptions / Screening Tool to Alert to Right Treatment). This tool lists clinical scenarios where specific medications should be stopped due to high risk or explicitly started because they are under-utilized.

Medications that have been identified as potentially harmful should be discontinued unless there are no clinical alternatives and the medication provides appropriate benefit to the patient. Inform the patient’s other providers of any medication changes (NCCMERP, 2026).

Ensure medication side effects and toxicities are included in the differential diagnosis of every new symptom until ruled out. Use a risk versus benefit approach to find the most appropriate therapy given the patient’s values and ability to adhere to the chosen regimen (NCCMERP, 2026).

2.2.2 Surgical and Procedural Errors

Surgical and procedural errors are treatment errors that can occur as a result of breakdowns in communication, fatigue, and understaffing, issues related to poor surgical planning. The most common surgical errors are:

• wrong site / wrong procedure / wrong patient surgeries
• accidentally leaving a foreign object in a person after surgery
• accidentally lacerating a nearby organ during surgery or misplacing a medical device

Wrong site/wrong procedure/ wrong patient surgical errors usually stem from communication failures, a rushed environment, or a breakdown in the preoperative verification process. They are considered to be entirely preventable.

The most common type of wrong site event occurs when the correct procedure is performed on the correct patient, but at the wrong anatomic location. For example, removing the left kidney instead of the right, the wrong finger or toe, or operating on the wrong vertebrae. The most common causes are preoperative failing to mark the surgical site physically, misinterpreting flipped diagnostic radiology images, or relying on standard “left/right” charting notes without confirming with the patient.

Accidentally leaving a foreign object inside a patient after closing a surgical incision is formally known as a Retained Foreign Object (RFO) or a Retained Surgical Item (RSI). Like wrong-site surgeries, it is classified as a Never Event—a serious, preventable medical error that indicates a major breakdown in hospital safety systems.

Items left behind during surgery are usually materials that easily blend into wet human tissue. Surgical sponges account for a large percentage of foreign objects left behind after surgery. This is because sponges become saturated with blood, mimicking the color, texture, and feel of internal organs, making them incredibly difficult to spot visually inside an open surgery.

Surgical instruments such as clamps, forceps, retractor components, and scissors are more likely to be left behind during deep-cavity surgeries or massive chest/abdominal procedures. Small hardware and fragments such as needles used for suturing, catheter tips, guide wires, or broken pieces of surgical drill bits and blades can also be left behind.

Accidental laceration of a nearby organ (iatrogenic perforation) and the misplacement of a medical device are two distinct types of surgical complications. While they are sometimes completely accidental due to complex patient anatomy, they frequently stem from blind insertion techniques, improper imaging verification, or mechanical miscalculations.

Unlike Never Events (such as operating on the wrong leg), accidental cuts or device misplacements are recognized risks of complex procedures. However, their timely recognition and repair is what separates a manageable complication from a life-threatening crisis.

2.2.3 Equipment and Technology Failures

Equipment and technology failures occur when devices fail or are improperly programmed or when devices subtly differ between manufacturers. While technology is designed to reduce error, it frequently introduces new, unforeseen failure modes. For example:

• Alert fatigue can occur when the electronic health record (EHR) system triggers meaningless pop-up warnings for every minor drug interaction. This can cause clinicians to subconsciously click through critical, life-saving alerts.
• Poor human-factors engineering occurs when medical devices have non-intuitive user interfaces, identical-looking packaging for entirely different medications (look-alike/sound-alike drugs), or confusing menu structures on IV smart pumps.
• System interoperability issues can occur when a laboratory system doesn't seamlessly push critical values into a provider's mobile and stalls delivery of time-critical interventions (like sepsis protocols) stalls.

Adverse events involving medical devices can also be caused by technical malfunction, improper use, inadequate maintenance, or the patient’s clinical condition. Given this complexity, each event should prompt an investigation to identify the root cause, ensure accountability, and prevent recurrence (Mishali et al., 2025).

Identifying the root cause of a medical error is not always straightforward. When the cause is unclear, parties may seek to distance themselves from responsibility: healthcare professionals may attribute the problem to a device malfunction, while manufacturers, who invest heavily in designing reliable equipment, often emphasize issues related to maintenance or use (Mishali et al., 2025).

2.2.4 Monitoring and Delay Failures

Missing early, progressive signs of clinical deterioration is a common and damaging failure in inpatient medical care. This phenomenon is widely known as Failure to Rescue (FTR).

Failure to rescue does not mean the clinician actively caused a new injury (like an accidental surgical laceration). Instead, it means the healthcare system failed to recognize and react to a patient who was slowly and predictably breaking down from an underlying condition, such as internal bleeding, respiratory failure, or sepsis.

The most common drivers of clinical deterioration are sepsis, arrythmias, congestive heart failure/volume overload, hypoxemia, electrolyte abnormalities, hypovolemia, and hemorrhage. The early signs of deterioration include changes in respiratory rate, oxygen saturation, blood pressure, heart rate, temperature and conscious/mental status which may go unrecognized.

2.3 Prevention Errors

Prevention errors involve the failure to implement appropriate preventive measures, such as vaccination or disease screening programs, potentially increasing the risk of complications and preventable diseases. Prevention errors are particularly common in acute care hospital settings, long-term care facilities, and outpatient preventative medicine.

The most common types of prevention errors:

• Hospital-aquired conditions such as pressure ulcers, deep vein thrombosis, or pulmonary embolisms.
• Healthcare-associated infections such as Catheter-Associated Urinary Tract Infections (CAUTIs) and Central Line-Associated Bloodstream Infections (CLABSIs).
• Outpatient and screening failures: missed screenings, inadequate follow-up care, and missed immunizations.

2.4 Communication Errors

Communication failure is cited by The Joint Commission as a root cause for the majority of serious adverse events and sentinel events. Shift changes, handoffs, and transitions in care are a common source of communication breakdowns, which can include:

• failures in communication between healthcare providers and patients
• inter-professional communication breakdowns
• misunderstandings and erroneous clinical decisions
• vague verbal orders, poorly written orders, mishearing an order
• hierarchical barriers, discomfort questioning another provider’s decisions
• dropping crucial information during shift changes or transfers between departments

It is crucial to recognize that medical errors are not usually the result of negligence or incompetence. Rather, they often arise from complex interactions among multiple factors, including healthcare system limitations, resource constraints, personnel fatigue, care delivery pressures, and cognitive biases (Sanchez and Corvalan, 2025).

2.5 Environmental and Organizational Factors

The structural framework of the facility itself dictates how safely care can be delivered. Understaffing, high workloads, and high nurse-to-patient ratios restrict the time a clinician can dedicate to double-checking high-alert medications or properly monitoring high-fall-risk individuals.

Physical workspace design such as poor lighting in medication rooms, noisy environments that induce alarm fatigue, or disorganized supply carts all create physical bottlenecks that invite errors. When a “blame” culture punishes individuals for honest system-driven mistakes, staff will hide near-misses. Without reporting, the organization cannot address system weaknesses before they lead to real patient harm.