Background: Patients with chronic obstructive pulmonary disease (COPD) have elevated serum levels of ultrasensitive C reactive protein (CRPus). This raise may be related directly to COPD and its associated systemic inflammation or secondary to other factors such as smoking status, disease severity, acute exacerbations, or associated complications.
Aim: To evaluate the potential causes of raised levels of CRPus in stable COPD patients.
Patients and methods: Cohorts of 133 mild-to-very severe COPD patients (41 current smokers), 31 never-smokers, and 33 current smoker controls were compared. Clinical assessments included body mass index (BMI), fat (FM) and fat-free mass (FFM) measurement by DEXA, forced expiratory volume in one second (FEV1), arterial oxygen tension (PaO2), six-minute walking test (SMWT), emphysema (EMPH) and right thigh muscle cross-sectional area (TMCSA), both quantified by high resolution computed tomography.
Results: Serum CRPus levels were significantly higher in COPD patients than in controls (7 ± 4.2 and 3.7 ± 2.7 mg/L respectively; p < 0.0001). Being smoker did not influence CRPus levels. These levels were significantly correlated with FM (r = 0.30), BMI (r = 0.21), FEV1 (r = -0.21), number of acute exacerbations of the disease in the last year (r = 0.28), and PaO2 (r = -0.27). Using multivariate analysis FM, PaO2, and number of acute exacerbations of the disease in the last year had the strongest association with CRPus levels.
Conclusions: CRPus is elevated in COPD patients, independent of smoking status. It is weakly associated with fat mass, arterial oxygen tension and frequency of exacerbations.