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What’s New in the Patient Safety World

August 2019

How Often Do Preventable Errors Occur?



The 1999 Institute of Medicine (IOM) report “To Err is Human: Building a Safer Health System” has widely been recognized as opening the eyes of the public and the medical profession about the enormity of the issue of medical errors. It estimated that up to 98,000 patients might die each year as the result of their medical care rather than from their underlying medical conditions. While some criticized the study as overestimating the numbers or noted many of the patients may have died anyway, most of us who have been hospital medical directors or been involved in quality improvement and patient safety felt the numbers were likely underestimates.


Since then there have been numerous studies looking at the frequency of medical errors, but most have focused on total errors rather than those errors that are truly preventable.


A new systematic review and meta-analysis in the BMJ concludes that around one in 20 patients are exposed to preventable harm in medical care (Panagioti 2019). Moreover, 12% of such cases result in permanent disability or death.


The authors reviewed 70 studies, with over 300,000 patients, that reported on preventable harm. The pooled prevalence for preventable patient harm was 6%. And the pooled prevalence of overall harm (preventable and non-preventable) was 12%. A pooled proportion of 12% of preventable patient harm was severe or led to death. The highest percentage of incidents with preventable harm were related to drugs (25%) and other treatments (24%), followed by surgical procedures (23%), healthcare infections (16%,), and diagnosis (16%).


Since the authors found preventable patient harm occurs in 6% of patients across medical care settings and the pooled prevalence of overall harm was 12%, the authors conclude that half of patient harm is preventable.


Compared with general hospitals (where most evidence originated), preventable patient harm was more prevalent in advanced specialties (intensive care or surgery). The highest pooled prevalence estimate of preventable patient harm was reported in intensive care (18%) and surgery (10%) and the lowest in obstetrics (2%).


In addition to the human costs, the authors note that preventable harm results in about $9.3 billion in extra health care costs in the United States. That comes from a study by Zhan et al. (Zhan 2003) which studied excess length of stay, charges, and mortality attributable to medical injuries during hospitalization. From their data, they extrapolated to infer that the 18 types of medical injuries studied may add to a total of 2.4 million extra days of hospitalization, $9.3 billion excess charges, and 32,591 attributable deaths in the United States annually.


Two accompanying editorials (Abbasi 2019, Papanicolas 2019) discuss the heterogeneity of definitions of preventable harm across studies and call for better measures of preventable harm.


In an upcoming column we will discuss the recent analysis by the Betsy Lehman Center for Patient Safety in Massachusetts of the financial costs of medical errors and the behavioral, physical, emotional, and financial harms to those who suffered the errors (Betsy Lehman Center 2019). Overall, they identified almost 62,000 preventable harm events that resulted in over $617 million in excess health care insurance claims. That accounts for about 1% of the total Massachusetts expenditures on healthcare in 2017.


Landrigan et al (Landrigan 2010) found lethal adverse events due to medical errors in 0.6% of hospital admissions in North Carolina hospitals, 63.1% of which were deemed to be preventable.


Other studies put the estimates for patient harm resulting from healthcare at much higher rates. In our May 2011 What’s New in the Patient Safety World column “Just How Frequent Are Hospital Medical Errors?” we noted a study (Classen 2011), using IHI’s Global Trigger Tool to identify hospital adverse events, that found that the numbers may be 10-fold higher than what was noted in the IOM report. Potentially avoidable adverse events occurred in a third of hospital admissions. Another study by Levinson (Levinson 2012) found that hospital incident reporting systems do not capture most patient harm.


James (James 2013) utilized the Global Trigger Tool (GTT) methodology to identify cases of potentially preventable medical errors. Using a weighted average of 4 studies utilizing the GTT, he estimated that the lower limit of deaths per year associated with preventable harms in hospitals is 210,000 deaths per year. And, given the limitations of the GTT and fact that these studies did not include deaths related to diagnostic errors which may not show up for years, he further estimated that the number of deaths associated with preventable harm may be more than 400,000 per year. He also noted that the frequency of serious harm may be 10- to 20-fold higher than that for lethal harm.


Makary and Daniel (Makary 2016) declared medical errors as the third leading cause of death in the US but pointed out the great difficulties in accurately measuring this problem.


How dangerous is a day in the hospital? For many years, we have used the numbers from a study done by Lori Andrews et al. (Andrews 1997) that found you have a 6% chance per inpatient day of having an adverse event that could impact your health. And, of course, a 2010 report (Levinson 2010) showed that one in every seven Medicare patients who is hospitalized experienced adverse events during their hospital stays, up to 44% being potentially preventable. A study (Hauck 2011) quantified the risk even further. Using a large database from public hospitals in Australia, the authors calculated that the average hospital stay carries a 5.5% risk of adverse drug reaction, 17.6% risk of infection, and 3.1% risk of pressure ulcers. Moreover, each additional night in the hospital increases the risk by 0.5% for adverse drug reactions, 1.6% for infections, and 0.5% for pressure ulcers.



So, got all those numbers? You’ll forget them shortly. You’ve often heard us use the phrase “Stories, Not Statistics” (see our December 2009 What’s New in the Patient Safety World column “Stories, Not Statistics”). When we first began doing presentations on patient safety in the early 1990’s we often began with some of the statistics on medical error from Lucien Leape’s work. But we began to notice physicians and medical students begin to zone out when we talked about statistics on medical error. What got their attention were the anecdotes we would tell about cases that really happened. So, we changed our focus. While we still often show statistics on medical error to put things in context, we no longer highlight them. Instead, we really rely on the stories. That’s what makes people say “I wonder if that could happen here?” and what makes them go back to look at the systems in their health care systems. It is those stories that hit home hard and make people remember. Who cannot remember their own reactions when they first heard the Josie King story, or the story about the nurse who administered Bicillin intravascularly, or the little boy who died from concentrated epinephrine injection during a simple surgical procedure, or any nurse who inadvertently administered concentrated potassium solutions?


In fact, the lack of compelling stories like these is the prime reason we feel IOM’s “To Err is Human: Building a Safer Health System” failed to gain traction despite considerable initial media attention. Everyone focused on the statistics from that report. It lacked the stories about real people you need to tell in order to get people and systems to change.


The new Panagioti study will undoubtedly suffer the same fate. Yes, it does reinforce the magnitude of the problem. But telling stories about real people experiencing such problems is what will get your healthcare colleagues to perk up and take notice that many of those problems could happen in their hospital or their practice.




See some of our prior columns on the frequency of harmful medical errors:


May 2011                    “Just How Frequent Are Hospital Medical Errors?

February 2012             “OIG: Hospitals Fail to Recognize Most Cases of Harm

March 2012                 “How Dangerous is a Day in the Hospital?

October 2013              “How Many Deaths Result from Medical Errors?







Institute of Medicine. To Err is Human: Building a Safer Health System. Washington, DC: National Academy Press, 1999



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; 36: l4185



Zhan C, Miller MR. Excess length of stay, charges, and mortality attributable to medical injuries during hospitalization. JAMA 2003; 290: 1868-1874



Abbasi K. First do no harm: the impossible oath.  BMJ 2019; 366: l4734



Papanicolas I, Figueroa JF. Preventable harm: getting the measure right. BMJ 2019; 366 : l4611



Betsy Lehman Center for Patient Safety. The Financial and Human Cost of Medical Error... and how Massachusetts can lead the way on patient safety. Betsy Lehman Center 2019; June 2019



Landrigan CP, Parry GJ, Bones CB, et al. Temporal Trends in Rates of Patient Harm Resulting from Medical Care. N Engl J Med 2010; 363: 2124-2134



Classen D, Resar R, Griffin F, et al. ‘Global Trigger Tool’ Shows That Adverse Events In Hospitals May Be Ten Times Greater Than Previously Measured. Health Affairs 2011; 30(4): 581-589



Levinson DR. OIG (Office of the Inspector General. Department of Health and Human Services). Hospital Incident Reporting Systems Do Not Capture Most Patient Harm. January 2012



James JT. A New, Evidence-based Estimate of Patient Harms Associated with Hospital Care. Journal of Patient Safety 2013; 9(3): 122–128,_Evidence_based_Estimate_of_Patient_Harms.2.aspx



Makary MA, Daniel M. Medical error-the third leading cause of death in the US. BMJ 2016; 353: i2139



Andrews LB, Stocking C, Krizek T, et al. An alternative strategy for studying adverse events in medical care. Lancet 1997; 349: 309–313



Levinson DR. Adverse Events in Hospitals: National Incidence Among Medicare Beneficiaries. Washington, DC: US Department of Health and Human Services, Office of the Inspector General; November 2010. Report No. OEI-06-09-00090



Hauck K, Zhao X. How Dangerous is a Day in Hospital?: A Model of Adverse Events and Length of Stay for Medical Inpatients. Medical Care 2011; 49(12): 1068-1075, December 2011






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