C-reactive protein levels predict bacterial exacerbation in patients with chronic obstructive pulmonary disease.

Background: Chronic obstructive pulmonary disease (COPD) causes a high rate of morbidity worldwide and predicting a bacterial cause of an exacerbation of COPD is difficult.

Method: In this study, patient serum was obtained and C-reactive protein (CRP) levels were measured using an automated latex-enhanced turbidimetric assay. Sputum samples were obtained and evaluated microscopically. The relationship between CRP and the bacterial colonies in sputum in 81 patients with an exacerbation of COPD was assessed. Receiver operating characteristic (ROC) curves and the respective areas under the curve (AUCs) were calculated. Data from 64 patients with bacterial acute exacerbation of COPD (AECOPD) were compared with those of 37 patients with no documented bacterial AECOPD. Results categorized according to the nature of sputum as mucoid or purulent were also compared.

Results: High median CRP levels were observed in bacterial AECOPD compared with nonbacterial AECOPD. The ideal cutoff point for distinguishing patients with bacterial AECOPD from those with nonbacterial AECOPD was 19.65 mg/L (sensitivity, 78.18%; specificity, 84.61%; AUC, 0.832). In patients with mucoid sputum, the cutoff point was 15.21 mg/L and the area under the ROC curve 0.86, with a sensitivity of 81.5% and a specificity of 77.8%. Purulent sputum had a significantly higher CRP level than mucoid sputum, but with an AUC of only 0.617 (95% confidence interval, 0.49-0.74) to diagnosis bacterial AECOPD.

Conclusions: In adult patients with symptoms of AECOPD, an elevated serum CRP level of >19.6 mg/L indicates bacterial exacerbation. In patients with AECOPD with mucoid sputum, an elevated CRP level of >15.21 mg/L indicates bacterial infection, which may be a useful clinical marker for therapy of this disease.