Procalcitonin vs C-reactive protein as predictive markers of response to antibiotic therapy in acute exacerbations of COPD.

Rational prescription of antibiotics in acute exacerbations of COPD (AECOPD) requires predictive markers. We aimed to analyze whether markers of systemic inflammation can predict response to antibiotics in AECOPD. We used data from 243 exacerbations out of 205 patients from a placebo-controlled trial on doxycycline in addition to systemic corticosteroids for AECOPD. Clinical and microbiologic response, serum C-reactive protein (CRP) level (cutoffs 5 and 50 mg/L), and serum procalcitonin level (PCT) (cutoffs 0.1 and 0.25 μg) were assessed. Potential bacterial pathogens were identified in the majority of exacerbations (58%). We found a modest positive correlation between PCT and CRP (r = 0.46, P < .001). The majority of patients (75%) had low PCT levels, with mostly elevated CRP levels. Although CRP levels were higher in the presence of bacteria (median, 33.0 mg/L [interquartile range, 9.75-88.25] vs 17 mg/L [interquartile range, 5.0-61.0] [P = .004]), PCT levels were similar. PCT and CRP performed similarly as markers of clinical success, and we found a clinical success rate of 90% in patients with CRP ≤ 5 mg/L. A significant effect of doxycycline was observed in patients with a PCT level < .1 μg/L (treatment effect, 18.4%; P = .003). A gradually increasing treatment effect of antibiotics (6%, 10%, and 18%), although not significant, was found for patients with CRP values of ≤ 5, 6-50, and > 50 mg/L, respectively. Contrary to the current literature, this study suggests that patients with low PCT values do benefit from antibiotics. CRP might be a more valuable marker in these patients.