C-reactive protein levels in stable COPD patients: a case-control study

Background: Previous studies have documented that C-reactive protein (CRP) levels are increased in stable COPD patients. However, most studies have also shown that higher CRP levels are observed in patients with comorbidities like diabetes mellitus and cardiovascular disease. We aimed to investigate if CRP levels are increased in stable COPD patients, and if there is an association between CRP levels and pulmonary function tests and clinical characteristics. Methods: We conducted a case-control study in a tertiary care, university-affiliated hospital. COPD patients and controls were matched for sex and age in a 2: 1 matching ratio. We included only those patients who had quit smoking. CRP levels were determined and pulmonary function tests were performed in both the groups. Results: A total of 60 COPD patients and 30 controls were included in the analysis. The study subjects had a mean age of 64.8+/-8.5 years in COPD group and 64.3+/-9.2 years in control group (P=0.214). The median of CRP levels was 3.17 mg/L (interquartile range [IQR]: 1.73-5.99 mg/L) in COPD group and 2.13 mg/L (IQR: 1.18-7.69 mg/L) in control group (P=0.370). There were 34 (56.7%) patients in COPD group and 14 (46.7%) patients in control group with CRP levels greater than 3 mg/dL (P=0.382). Using bivariate correlations, we found significant positive correlations in COPD patients between body mass index (BMI) and CRP (r=0.3, P=0.045), and between CRP and forced vital capacity (FVC, % of predicted) (r=-0.3; P=0.023). In a multivariate model, female sex and FVC (% of predicted) were associated with a CRP value greater than 3 mg/dL in the COPD group. Conclusion: The levels of CRP in the stable COPD patients were not significantly different when compared to those in the control subjects. Female sex and FVC (% predicted) were associated with CRP levels greater than 3 mg/dL in the COPD group.