A validation and potential modification of the pneumonia severity index in elderly patients with community-acquired pneumonia

OBJECTIVES: To evaluate the discriminatory power of the Pneumonia Severity Index (PSI) in elderly patients with community-acquired pneumonia (CAP) and to improve its performance. DESIGN: Retrospective review of 193 patients from 1999 to 2001 to derive prognostic rules. The rules were prospectively validated in 144 patients from 2002 to 2003. SETTING: Iwata City Hospital, a 400-bed general hospital. PARTICIPANTS: Patients aged 80 and older who had CAP and were admitted to the hospital. MEASUREMENTS: Predictors of 30-day mortality were identified using logistic regression analysis, and several rules were constructed by combining the PSI and the independent predictors. RESULTS: The original PSI, which defines PSI Class IV and V as a high-risk group, did not perform well in discriminating survivors from nonsurvivors (sensitivity 100%, specificity 15%), whereas a modified PSI, which defines only PSI Class V as a high-risk group, performed better (sensitivity 86%, specificity 63%). Three predictors for mortality were identified independent from the modified PSI: performance status (PS) Grade 3 or higher, anorexia, and partial pressure of carbon dioxide of 50 mmHg or greater. By combining the modified PSI and PS, the performance could be further improved (sensitivity 79%, specificity 80%). CONCLUSION: The modified PSI could identify low-risk patients more accurately than the original PSI. In addition, by combining the modified PSI with PS, higher performance was obtained. Such information would aid physicians in clinical decision-making without overestimating the risk for elderly patients with CAP.