Background: Far from all patients with exacerbation of chronic obstructive pulmonary disease (COPD) benefit from antibiotic treatment. However, as these patients are often colonized with bacteria, even in a stable phase, there is no reliable method for establishing whether the patients have a significant bacterial infection and would benefit from antibiotic treatment. C-reactive protein (CRP) has proven to be useful as a marker of bacterial infection. The aim of this study was to assess to what degree CRP is elevated in patients with exacerbation of COPD.
Methods: A total of 166 consecutive patients admitted to a department of internal medicine at a university hospital in Copenhagen due to exacerbation of COPD were prospectively included in the study. Patients were asked whether they had experienced increased sputum purulence and whether they were on steroid treatment or not. Blood was drawn for determination of white blood cell count and CRP, and a chest X-ray was taken. Patients whose X-rays of the thorax showed changes compatible with pneumonia were considered to have pneumonia of bacterial origin.
Results: Pneumonia was diagnosed in 51 patients. Their median CRP was 97 mg/l (49-145 interquartile range). Among patients without pneumonia, 46% (51/115) had normal CRP values (0-10 mg/l); 64 had no increased sputum purulence and a median CRP of 8 mg/l (2.9-16 mg/l), which is significantly lower than in the 51 patients who reported increased sputum purulence and had a CRP of 45 mg/l (8.5-86 mg/l; p<0.001).
Conclusion: CRP values are normal in nearly 50% of patients admitted due to exacerbation of COPD. In patients who have increased sputum purulence, the pattern of increase in CRP is similar to that seen in patients with pneumonia. This suggests that CRP may be used as a marker of significant bacterial infection. Thus, it may be used when deciding whether or not to start antibiotic treatment. This should be tested in a controlled trial.