In 1999, the Institute of Medicine published a report entitled, “To Err Is Human,” that estimated 44,000 to 98,000 patients die annually in hospitals due to medical error.¹ In 2016, a sensational publication claimed medical error as the third-leading cause of death in the United States.² Now, a new systematic review published by the Agency for Healthcare Research and Quality (AHRQ) has put the emergency department (ED) in its crosshairs.³

This AHRQ review claims diagnostic error occurs in nearly one in 18 ED patients, resulting in 2.6 million adverse events with 370,000 serious harms, including 250,000 deaths. The response to this article has been swift, with all the major emergency medicine professional societies signing on to a response conveying their dismay.⁴ This dismay is not grounded in the harsh focus on the state of emergency medicine practice, but on the flawed analysis itself.

The core issues repeatedly raised involve the studies used to estimate the frequency of diagnostic error. The authors of the AHRQ review generate their estimate from three small studies examining the outcomes of a mere 1,758 patients in Spain, Switzerland, and Canada.

Two of these studies form the basis for their estimate of the rate of diagnostic error occurring in the ED. Only one of these studies specifically measures error in those discharged from the ED. This study was conducted over 15 years ago in Tenerife, in the Canary Islands, an archipelago off the coast of Morocco and collectively administered as an autonomous community of Spain.⁵ It reviewed outcomes of 500 patients, specifically selecting half from those having an unscheduled 72-hour return to the ED. The practice environment differed substantially from the U.S., with nearly 90 percent of patients evaluated by residents and non-emergency physician staff, with these physicians averaging three patients per hour in a seasonally overcrowded department. Blood tests were performed on only approximately half of patients and CTs on a mere two percent.

Within the cohort of unscheduled 72-hour returns, 20 percent displayed discordant diagnoses between initial and subsequent ED visits, while those without unscheduled returns displayed a four percent rate of discordant diagnoses at primary health center follow-up. Even if the decades-old performance of this remote archipelago were a reasonable proxy for modern U.S. medical care, it is immediately obvious a discrepantly coded diagnosis is not a reliable surrogate for diagnostic error. A handful of core definitions of diagnostic error exist, including one from the National Academy of Medicine, and each requires full case review to determine missed or delayed opportunities to make a correct or timely diagnosis.⁶ Absent any sort of structured review, no accurate estimate for the rate of diagnostic error can be ascertained.