Procalcitonin levels and bacterial aetiology among COPD patients admitted to the ICU with severe pneumonia: a prospective cohort study

Background: Serum procalcitonin (PCT) is considered useful in predicting the likeliness of developing bacterial infections in emergency setting. In this study, we describe PCT levels overtime and their relationship with bacterial infection in chronic obstructive pulmonary disease (COPD) critically ill patients with pneumonia. Methods: We conducted a prospective cohort study in an ICU of a University Hospital. All consecutive COPD patients admitted for pneumonia between September 2005 and September 2006 were included. Respiratory samples were tested for the presence of bacteria and viruses. Procalcitonin was sequentially assessed and patients classified according to the probability of the presence of a bacterial infection. Results: Thirty four patients were included. The PCT levels were assessed in 32/34 patients, median values were: 0.493 mu g/L [IQR, 0.131 to 1.471] at the time of admission, 0.724 mu g/L [IQR, 0.167 to 2.646] at six hours, and 0.557 mu g/L [IQR, 0.123 to 3.4] at 24 hours. The highest PCT (PCTmax) levels were less than 0.1 mu g/L in 3/32 (9%) patients and greater than 0.25 mu g/L in 22/32 (69%) patients, suggesting low and high probability of bacterial infection, respectively. Fifteen bacteria and five viruses were detected in 15/34 (44%) patients. Bacteria were not detected in patients with PCTmax levels <0.1 mu g/L. In contrast, bacteria were detected in 4/7 (57%) patients estimated unlikely to have a bacterial infection by PCT levels (PCTmax >0.1 and <0.25 mu g/L). Conclusion: Based on these results we suggest that a PCT level cut off >0.1 mu g/L may be more appropriate than 0.25 mu g/L (previously proposed for non severe lower respiratory tract infection) to predict the probability of a bacterial infection in severe COPD patients with pneumonia. Further studies testing procalcitonin-based antibiotic strategies are needed in COPD patients with severe pneumonia.