Background Patients with community-acquired pneumonia (CAP) often require hospitalisation. CRB-65 is a simple and useful scoring system to predict mortality. However, prognostic factors such as underlying disease and blood oxygenation are not included despite their potential to increase the performance of CRB-65.

Methods The study included 1172 consecutive patients (830 inpatients, 342 outpatients) with CAP. Mortality, sensitivity, specificity, positive predictive value and negative predictive value, and the area under the receiver operating characteristic (ROC) curve with 95% CI were calculated. Prognostic accuracy was evaluated after adding coexisting illnesses according to the Pneumonia Severity Index (malignancy, heart failure, hepatic, renal and cerebrovascular disease) and pulse oximetry (SpO₂).

Results Mean age was 65 years, 30-day mortality 7% (inpatients 9%, outpatients 1%). Addition of one point for the presence of ≥1 coexisting condition and one point for SpO₂ <90% increased the area under the ROC curve of CRB-65 from 0.82 (95% CI 0.77 to 0.85) to 0.87 (95% CI 0.84 to 0.90; p<0.0001).

Conclusions Modification of CRB-65 by including hypoxaemia and presence of specified underlying diseases increased the scoring system’s prognostic accuracy while retaining its independence of laboratory tests. DS CRB-65 may have the potential to further facilitate site of care decision for patients with CAP.