It has been well over a year since the controversial publication of the Agency for Healthcare Research and Quality (AHRQ) report on diagnostic errors in the emergency department (ED).¹ The striking conclusions of this report included estimates that 0.1 to 0.4 percent of ED visits resulted in preventable death as result of diagnostic error. While these percentages appear small, when multiplied by the 130 million ED visits annually, these authors arrive at an estimate of 250,000 preventable deaths. Adding in errors and preventable deaths in those occurring following admission to the hospital, these same authors now propose up to 371,000 deaths annually in the United States as a direct consequence of diagnostic error.² This accounts for nearly 15 percent of all deaths annually in the United States alone.

Putting aside, for a moment, the methods leading to concerns regarding the magnitude of these estimates, the fact remains diagnostic errors occur with under-appreciated frequency. The better questions remain: Where in the process of care do the harmful errors occur? If these can be characterized, what preventive interventions might be considered?

Taking a different approach than the authors of the AHRQ report, Auerbach et al used a “look back” approach to perform both qualitative and quantitative evaluations of the types and frequencies of errors occurring in hospital settings.³ In their study, patients were identified retrospectively as having suffered deterioration following admission resulting in transfer to the intensive care unit, death, or both. From their initial search, the authors found 2,428 patients meeting criteria, for each of whom they performed manual chart review. Of these, the authors identified 550 (23.0 percent) patients had experienced a diagnostic error. As a “look back method,” these are not estimates for the overall prevalence of error but do provide substantial sample size for their analyses of subtypes of diagnostic error.

By far, the most common subtypes of diagnostic error were those associated with patient assessment and obtaining appropriate testing. The bulk of patient assessment errors fell into the category of failure or delay to consider the diagnosis. The included example describes a critically ill patient admitted with hepatitis and hematochezia whose acidosis failed to improve with initial inpatient management. After developing encephalopathy and hypoxemic respiratory failure, the patient was transferred to the ICU. Further diagnostic testing in the ICU identified salicylate toxicity. In this case, the harm resulted directly from the initial failure to consider the correct diagnosis. It ought further to be noted, as with many cases of diagnostic error, several other types of error were identified as contributing to the primary error causing harm.