An Index of Daily Step Count and Systemic Inflammation Predicts Clinical Outcomes in Chronic Obstructive Pulmonary Disease

Abstract Background Identification of persons with chronic obstructive pulmonary disease (COPD) at risk for acute exacerbations (AEs) targets them for close monitoring. Objectives We examined the ability of a novel index combining physical activity and systemic inflammation to identify persons at risk for AEs. Methods In an observational cohort study of 167 persons with COPD, we assessed daily step count, a direct measure of physical activity, with the StepWatch Activity Monitor and measured plasma C-reactive protein (CRP) and IL-6 levels. AEs and COPD-related hospitalizations were assessed prospectively over a median of 16 months. Predictors of AEs and COPD-related hospitalizations were assessed using negative binomial models. Measurements and Main Results Median daily step count was 5,203 steps (interquartile range, 3,627–7,024). Subjects with daily step count ≤ 5,203 and CRP > 3 mg/l had an increased rate of AEs (rate ratio [RR], 2.06; 95% confidence interval [CI], 1.30–3.27) and COPD-related hospitalizations (RR, 3.51; 95% CI, 1.73–7.11) compared with subjects with daily step count > 5,203 and CRP ≤ 3 mg/l, adjusting for FEV1% predicted and prednisone use for AE in the previous year. Similarly, subjects with daily step count ≤ 5,203 and IL-6 > 2 pg/ml had an increased rate of AEs (RR, 2.04; 95% CI, 1.14–3.63) and COPD-related hospitalizations (RR, 4.27; 95% CI, 1.56–11.7) compared with subjects with daily step count > 5,203 and IL-6 ≤ 2 pg/ml. Conclusions An index combining daily step count and systemic inflammation can predict AEs and COPD-related hospitalizations. A validation study in a separate cohort is needed to confirm the utility of the proposed index as a clinical tool to risk stratify persons with COPD.