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About 6% of patients in healthcare settings internationally experience harm that could have been prevented. Around one in eight of these cases result in severe harm, causing permanent disability or death.

Drug errors, therapeutic management incidents and incidents involving invasive clinical procedures are the most common causes of preventable patient harm. Higher rates of harm were seen in intensive care and surgical departments than in general hospital settings.

This NIHR-funded review pooled data from observational studies carried out around the world. It was not possible to identify completely accurate rates of incidents and harm, due to differences in healthcare systems, and the methods and timeframes for reporting and analysing data. However, this well-conducted review provides the best evidence so far about the proportion of overall patient harm that could be prevented.

Studies came mainly from hospitals and will not have captured all harms in all settings. However, they indicate broad areas where action could be taken to prevent harm and reduce costs.


Why was this study needed?

Unintended harm to patients from the care they receive is one of the top 10 causes of disease burden across the world. This harm also results in a financial burden, with estimates of up to 15% of global healthcare budgets spent as a direct result of such events.

Not all incidents of patient harm can be avoided. For example, some people will react badly to drugs that are prescribed appropriately. However, some incidents are preventable.

Patient harm is classed as preventable if it happens as a result of an identifiable cause that could have been modified, and which could be avoided in future if processes are changed or guidelines adopted.

While there is previous research on overall patient harm, there is little specifically summarising rates of preventable patient harm. This study aimed to identify how often incidents happen across a range of healthcare settings, what types of incidents occur, and how severe those incidents are.


What did this study do?

This NIHR-funded systematic review pooled the results from 66 observational studies, published since January 2000. About three-quarters (76%) of the studies reviewed medical notes to detect preventable patient harm. The rest monitored patients over time or used self-reported data.

Most studies focused on adults, but six looked at children and adolescents, and five looked at older adults. Two-thirds of the studies were conducted in general hospitals. The rest took place in intensive care, surgery, emergency departments and obstetrics. Only three took place in primary care. Almost half the studies took place in the US, with six carried out in the UK.

The studies were assessed for quality and 41% were at low risk of bias. Case reviews did not necessarily capture all patient harm experienced and those using self-reported data were noted as being prone to increased risk of bias. Most studies reviewed past medical charts of samples of patients to identify errors and harm.


What did it find?

  • Overall, 6% of patients experienced preventable patient harm (95% confidence interval [CI] 5% to 7%; 66 studies, 337,025 participants).
  • Patients in intensive care had the highest prevalence of preventable patient harm at 18% (95% CI 12% to 26%; 6 studies), followed by patients undergoing surgery at 10% (95% CI 7% to 13%; 6 studies).
  • 12% (95% CI 9% to 15%; 20 studies) of preventable patient harm was classed as severe, as it caused permanent disability or patient death. About half (49%) was classed as mild and 36% as moderate.
  • Six types of patient harm were identified: drug management incidents (recorded in 25% of the preventable harm cases), other therapeutic management incidents (24%), procedural incidents (23%), surgical procedure incidents (23%), healthcare infections (16%), and diagnosis incidents (16%). Cases of harm could involve more than one type of harm.


What does current guidance say on this issue?

There is no single piece of national guidance on preventing patient harm.

NICE provides recommendations about the safe and effective use of drugs in its 2015 guideline on medicines optimisation. It also has several pieces of guidance on the prevention and control of healthcare-associated infections, including surgical site infections. NHS Improvement issue patient safety alerts to prompt and support organisations to take action.

NHS England and NHS Improvement published The NHS Patient Safety Strategy in July 2019. This describes how the NHS will continuously improve patient safety, including a new digital system to replace the National Reporting and Learning System. This is the mechanism for staff to report incidents wherever they work.


What are the implications?

This study suggests that over the last 20 years, around 6% of patients observed in studies have been harmed in incidents which could have been avoided. The incidents most commonly involve errors relating to medicines, other treatments or invasive procedures like surgery.

Action has been taken to improve systems and processes in some of these areas. These range from surgical safety checklists to ward-based pharmacists to identify prescribing errors. However, more can be done by organisations and staff to understand and act on preventable harms.

This study included little data from primary and community care, but highlights some of the main issues and types of preventable harm within hospital settings. The findings may help to develop strategies targeting these issues specifically.


Citation and Funding

Panagioti M, Khan K, Keers RN et al. Prevalence, severity, and nature of preventable patient harm across medical care settings: systematic review and meta-analysis. BMJ. 2019;366:l4185.

This project was funded by the UK General Medical Council (RMS 113361), and the NIHR Greater Manchester Patient Safety Translational Research Centre (GMPSTRC-2012-1) funded the first author’s time on the project.



NHS England and NHS Improvement. The NHS Patient Safety Strategy. London: NHS Improvement; 2019.

NHS Improvement. Patient safety alerts. London: NHS Improvement; last updated March 2018.

NICE. Medicines optimisation: the safe and effective use of medicines to enable the best possible outcomes. NG5. London: National Institute for Health and Care Excellence; 2015.

NICE. Prevention and control of healthcare-associated infections overview. NICE Pathway. London: National Institute for Health and Care Excellence; 2019.

WHO. 10 facts on patient safety. Geneva: World Health Organization; last updated August 2019.

Produced by the University of Southampton and Bazian on behalf of NIHR through the NIHR Dissemination Centre


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