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

Rationale: While 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. Methods: This 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. Results: Among 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). Conclusions: Over-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.