In this nationwide study of consecutive emergency episodes with relatively common diagnoses, DD was observed in 3.3% of hip fracture episodes and 8.5% of erysipelas episodes. DD had direct consequences for episode outcomes. Thus, 30-day readmission was increased by 45% for hip fracture episodes, and episode costs were increased by 79% for hip fracture episodes and 171% for erysipelas episodes. Senior physician employment at the ED – as opposed to external senior physicians being on call – appeared to be the strongest determinant of DD followed by decision authority and multidisciplinary team.
Several studies have assessed mechanisms leading to suboptimal diagnoses [1, 3, 5,6,7, 9]. One of these studies assessed organisational factors , finding that diagnostic errors were associated with system-related and cognitive factors. The former covered teamwork, for example, as also found in the present study. A few studies have assessed the potential consequences of DD and mainly assessed outcome in terms of costs, which they found to be increased [35, 36]. We also identified a recent study assessing consequences of DD in terms of health (in-hospital mortality) and quality of care (length of stay) . This study found both outcomes to be significantly increased among patients with DD. This study resembles our study in terms of methodology. Hence, both used the same definition of DD and both reported health and quality of care outcomes. However, we focused on 30-day outcome, whereas Hautz et al.  focused on outcomes during hospital stay only. In-hospital mortality was included in our 30-day measure, since it is recorded as from the day of diagnosis (hip fracture or erysipelas). The only cases in which in-hospital mortality would not be recorded are those where a patient is admitted more than 30 days after being given a diagnosis. However, even when also including 30-day post diagnosis outcomes, we still found no effect. The difference in mortality between the study by Hautz et al. and our study may therefore be due to other methodological differences such as size of study population, the single-centre nature of the study vs. national analysis, all ED diagnoses vs. selected ED diagnoses.
Definition of diagnostic discrepancy
A change in diagnosis is not always due to error. For erysipelas, a patient may be admitted to the ED with sepsis, which happened in 4.80% of erysipelas DD episodes. When this life-threatening condition is under control, the ED staff could conclude that sepsis was related to erysipelas, therefore changing the diagnosis to erysipelas. The same situation can be found in DD of hip fracture episodes; a hip fracture diagnosis requires x-ray to confirm the diagnosis. It can be discussed whether, e.g., first assigning the diagnosis S70.0 Contusion of hip (8.23%) or S32.5 Fracture of pubis (1.86%) is a flaw or just the natural order in which patients awaiting diagnostic imaging are diagnosed. Furthermore, the admission diagnosis is also influenced by the inherent uncertainty characterising patients’ symptom reporting, which is evidently also affected by their physical and/or mental state at admission. For example, delirium or unconsciousness may radically change patient-physician communication. Delirium is a condition commonly related to, e.g., pneumonia or dehydration , which was recorded as admission diagnoses among both patient groups (J18.9 pneumonia: hip fracture 1.78%, erysipelas 2.09%, E86.9 dehydration: hip fracture 1.65%, erysipelas 2.09%). Alternatively, DD may also arise if the main complaint is trouble breathing (related to pneumonia), and the physician observes that the patient also suffers from erysipelas. Even though patients with DD might not be assigned to the DD category due to diagnostic errors made by the ED staff, the DD definition still captures some patient complexity that can be difficult for ED staff to handle and which requires their attention in order to improve patient outcomes.
Possible explanation of study results
Emergency medicine has only recently (2017) been approved as a medical specialty in Denmark . Hence, during the study period, few senior physicians with emergency medicine competencies were available at EDs, and staff had few incentives to work at the ED and stay in this medical field [12, 16, 39]. During the study period, the EDs were therefore highly dependent on senior physician resources outside the ED. Seniors employed at the ED were primarily recruited from other specialties than emergency medicine (some senior physicians in emergency medicine could even have been recruited from abroad). Senior physician employment was found to be associated with DD, which could indicate a mismatch of ED resources, where seniors were diagnosing patients harbouring diseases that did not belong to their medical specialty. This is supported by previous studies indicating that diagnostic error occurs when information-processing capacity (e.g. clinical experience from the ED) does not match information-processing demands (e.g. ED patients in need of a diagnosis and treatment) [1, 40] and that DD was often related to faulty information processing . Thus, physicians will tend to look for information that confirms their intuition, and information that does not confirm this intuition will most often be rejected . Physicians’ intuition is based on pattern recognition memorised through medical training. An orthopaedic surgeon would therefore be likely to find patterns of orthopaedic diagnoses, whereas an emergency medicine physician would be expected to have an eye for acute conditions. Another aspect of this problem is that physicians have been found to be poor at self-assessing their ability to diagnose patients. This tendency was most outspoken among physicians who were least experts , whereas physicians with higher expertise where more capable of distinguishing easily diagnosed cases from more complex ones. Hence a solution to this problem would be to let experts handle patients, in this case seniors with competencies matching patients’ needs. This was also indicated by the negative association between DD and availability of external senior physicians, since they were called upon only when a patient’s symptoms matched the medical specialty of the external senior physician. Hopefully, emergency medicine senior physicians would soon also fulfil this expert role at the ED.
In the field of diagnostic error, this study is unique owing to its long study period and the inclusion of episodes encountered at several EDs (national analyses). Another strength is the complete survey data providing information about the organisational determinants of this study. However, our survey data have some limitations: the long study period might increase the risk of recall bias, and high staff turnover in the study period is expected to decrease the precision of the timeline construction, since the respondent might not have been affiliated with the ED during the whole study period. From our survey, we know when the EDs started to employ senior physicians, but we do not know the number of employed senior physicians and if this changed over time. Another limitation of this study is that we do not have all clinical data and therefore cannot go into further detail and determine whether DD was related to diagnostic error. The lack of detail also means that we have limited possibility to adjust for episode complexity, e.g. in the form of triage scores, although we adjusted for comorbidity and age.
The definition of the study cost perspective (episode costs) is both a strength (focus on ED services) and a limitation (lack of measures capturing the societal effect of DD). As opposed to the diagnosis-related grouping (DRG) tariff (based on national averages), the data on which this outcomes measure is based provide the number of available tariffs and thereby the actual variation in episode costs, which is a major strength. Unfortunately, this database suffers from missing data. Our mixed effect models are capable of handling missing data [29, 30].