Can Procalcitonin help to distinguish between an acute bacterial pneumonia and influenza A (H1N1) pneumonia on an intensive care unit?

Procalcitonin (PCT) is helpful for diagnosing bacterial infections. The diagnostic utility of PCT has not been examined thoroughly in critically ill patients with suspected H1N1 influenza. We prospectively assessed the clinical characteristics and PCT in patients admitted with lower respiratory tract infection to the medical intensive care unit (ICU) of the University hospital of Cologne during the 2009 and 2010 influenza seasons. Additionally, we performed a literature search to identify studies on the diagnostic role of PCT in ICU patients with suspected H1N1 influenza. Individual patient-data meta-analysis was conducted using data from our cohort (n = 46) combined with data from 5 eligible studies, with a total of 182 patients analyzed. PCT levels assessed during the first 48 hours after admission differed significantly between patients with and without bacterial pneumonia, but not H1N1 influenza status. The area under the curve of the ROC curve of PCT was 0.71 (95% CI 0.64 – 0.79, p < 0.0001) for diagnosis of bacterial pneumonia but increased to 0.76 (95% CI 0.68 – 0.84, p < 0.0001) when patients with hospital acquired pneumonia and immune-compromising disorders were excluded. A cut-off of procalcitonin of 0.5 µg/L had a sensitivity and a negative predictive value for diagnosis of bacterial pneumonia of 80.5% and 76.6% respectively, which increased to 85.5% and 84.6% in patients without hospital acquired pneumonia or immune-compromising disorder. In critically ill patients with suspected lower respiratory tract infection during the influenza season, PCT is a sensitive marker with high negative predictive value for detection of bacterial pneumonia particularly in patients with community acquired disease and without immune-compromising disorders.