Procalcitonin as a predictor of pneumonia in patients hospitalized with acute exacerbation of COPD: a prospective observational study

Background: Lower respiratory tract infection is the most common cause of acute exacerbations of COPD (AECOPD). The aim of the present study was to compare the accuracy of procalcitonin (PCT), C-reactive protein (CRP), and white blood cell count (WBC) as single diagnostic tests and in combination with clinical signs and symptoms to diagnose pneumonia in patients hospitalized with AECOPD. Methods: Prospective, single centre observational study. Patients with a spirometry confirmed COPD who were hospitalized due to AECOPD were consecutively recruited at the hospital’s Emergency Department. Pneumonia was defined as a new pulmonary infiltrate on chest X-ray. The values of PCT, CRP and WBC were determined at admission. Their accuracy in predicting a diagnosis of pneumonia was compared using receiver operating characteristic (ROC) curve analysis. The best combination of the variables to predict pneumonia was found using logistic regression. Results: Of the 118 included patients with AECOPD 38 (32%) had pneumonia at admission. PCT was significantly higher in samples from patients with pneumonia compared to those without pneumonia, median 0.1 vs. 0.05 mg/litre, p=0.001. The area under the ROC curve of PCT, CRP and WBC was 0.68, 0.73 and 0.66, respectively (p=0.42 for the test of difference). In a logistic regression model CRP, but not PCT was among the best predictor variables for pneumonia. Conclusion: As a single test PCT had about the same accuracy as CRP and WBC in diagnosing pneumonia in patients hospitalized with AECOPD and did not add to the diagnostic accuracy of the combination of relevant clinical parameters and CRP.