Understanding Diagnostic Uncertainty: Comparing Pre-Test Probability of Pneumonia to Bronchoalveolar Lavage Results in Critically Ill Patients

RationaleWhile clinical criteria are used to diagnose and treat pneumonia in critically ill patients, rates of concordance between a clinicians suspicion for pneumonia and a confirmed diagnosis using bronchoalveolar lavage (BAL) results are undefined. Factors that contribute to diagnostic concordance, and clinical outcomes associated with diagnostic discordance, are unknown. Objective(s)To assess rates of diagnostic concordance between clinicians pre-test probability of pneumonia and BAL-confirmed diagnosis, and to identify clinical factors and outcomes associated with diagnostic discordance in an intensive care unit (ICU) population. MethodsThis was a single-center, prospective observational study of intubated, mechanically ventilated patients. From 2018 to 2022, clinicians were asked to provide a pre-test probability of pneumonia on the same day they performed a bronchoalveolar lavage for the patient. ResultsAmong 659 patients, 84% (553/659) had pneumonia. Diagnostic concordance occurred in 80% (445/553) of these cases. Clinicians assigned a low pre-test probability for pneumonia to 20% (109/553) of patients with confirmed pneumonia. Clinicians assigned a high pre-test probability for pneumonia in 28% (30/106) of patients without pneumonia. Therefore, overdiagnosis in the setting of no pneumonia occurred more often than a missed diagnosis in the setting of true pneumonia (28% vs 20%, p = 0.05). Amongst patients with pneumonia, there were no significant differences in vital signs or laboratory values between those assigned a low pre-test probability of pneumonia and those assigned a high pre-test probability of pneumonia. In patients with culture negative pneumonia (n = 117), those assigned a low pre-test probability of pneumonia, compared to those assigned a high pre-test probability of pneumonia, had a longer length of stay in the hospital (36 days vs 18 days, p = 0.02) and the ICU (21 days vs 9 days, p = 0.01). ConclusionsOver-diagnosis, rather than a missed diagnosis, is the more frequent cause of diagnostic discordance. In culture-negative pneumonia, a low-pretest probability is associated with longer lengths of stay in the hospital and ICU. Future research should explore alternative approaches to improve diagnostic accuracy in critically ill patients.