A second study of patients admitted to the internal medicine service in Switzerland uses the same approach of looking for diagnostic discrepancies.⁷ Inselspital University Hospital in Berne, Switzerland, is a university hospital of approximately 40,000 annual visits staffed by an interdisciplinary unit within the ED, intensive care, and anesthesiology. In this study, clinicians reviewed ED admitting and IM discharge diagnoses to classify them as discrepant, clearly stating, “this study investigated discrepancies in diagnoses, not error, which would require a thorough review of the diagnostic process.” These authors ultimately identified discrepancies between admitting and discharge diagnoses in 12.3 percent of cases, three-quarters of which did not have the ED admitting diagnosis among the discharge diagnoses. The authors of the AHRQ review subsequently blend the diagnostic discrepancies from these two studies, from 15 years ago in the Canary Islands and seven years ago in Berne, Switzerland, to produce an overall 5.7 percent rate for diagnostic error in present-day U.S. EDs.

Attempting to Ascertain the Rate of Harm

The next portion of the AHRQ review uses these studies, and a third one from Canada, in an attempt to ascertain the rate of harm from diagnostic error.⁸ In the Canadian study conducted in 2004, follow-up was performed on 503 adult patients evaluated in “high acuity” areas of the ED. Of these patients, a single death was observed. A patient with chest pain was referred to cardiology with an elevated troponin level, but was subsequently diagnosed with, and died as a result of, an aortic dissection. As the sole “high-quality” study directly addressing the question of death from diagnostic error, this 0.2 percent estimate forms the foundation of all subsequent estimates.

A true 95 percent confidence interval from this study would generate an absurdly uninformative estimate of annual deaths attributed to diagnostic error ranging from 6,500 to 1.4 million. However, rather than admit this insurmountable limitation, the authors of the AHRQ review invent a new biostatistic, the “plausible range.” This made-up descriptor has no rigorous precedent, but rather represents an arbitrary ±2-fold range ultimately made up around the single death from aortic dissection observed in Canada.

To support this supposed “plausible range,” the authors construct increasingly specious chains of extrapolation from the small numbers of events in these studies from nearly 20 years ago, along with other mathematical calisthenics based on population-based death statistics. These other data are inappropriately elevated above observational studies conducted in ED populations, with estimates of death due to diagnostic error ranging from merely zero percent to 0.0074 percent.^9,10,11 With up to 1000-fold differences in estimates between data sources, the clear answer is the lack thereof: the true incidence and harms from diagnostic error across the heterogenous ED landscape in the U.S. remains unknown. It is irresponsible to publish an estimate and to assume such precision.