Role of serum interleukin-6 in detecting disease severity in chronic obstructive pulmonary disease patients

Background
Chronic obstructive pulmonary disease (COPD) is one of the leading causes of long-term illness and mortality on a global scale. Severe inflammation in the parenchyma, airways, and pulmonary vasculature is a hallmark of COPD. Chronic inflammation results in the irreversible constriction of small airways and the subsequent loss of alveolar walls (emphysema). In addition to the airway and lungs, research has shown that the inflammatory response was evident in the systemic circulating system.


Aim
This study’s purpose was to assess the role of serum interleukin-6 (IL-6) in detecting disease severity in patients with COPD.


Patients and methods
This is a case–control study that was conducted in the Chest Outpatient Clinic and Chest Department at Benha University Hospital. The study comprised two groups: group A included 40 patients with stable COPD. In group B, 40 people who appeared to be in good health served as the control group. An enzyme-linked immunosorbent assay was used to quantify serum IL-6 and spirometry was performed using the “Jaeger Master Screen PFT: CareFusion UK Ltd, Basingstoke, UK.”


Results
IL-6 serum levels (ng/l) were significantly higher (P<0.0001) in patients having COPD (241.10±114.79) compared with healthy controls (12.25±7.90). IL-6 revealed significant positive correlation with the smoking index (r=0.337, P=0.033) and high significant positive correlation with different stages of COPD (GOLD I–II–III–IV) (r=0.593, P<0.0001). However, it showed significant negative correlations with forced vital capacity (%) (r=−0.415, P=0.007), forced expiratory volume in the first second (%) (r=−0.505, P=0.0009), and forced expiratory flow 25–75% (r=−0.475, P=0.001). Furthermore, there was nonsignificant negative correlation between IL-6 and forced expiratory volume in the first second/forced vital capacity (%) (r=−0.233, P=0.174). IL-6 revealed a highly significant positive association with the modified Medical Research Council (r=0.693, P<0.0001) along with CAT assessment (r=0.793, P<0.0001), and number of exacerbations in previous year (r=0.438, P = 0.004), while it revealed significant Negative correlation with Body Mass Index (BMI) (r=−0.373, P = 0.017).


Conclusions
COPD patients had greater serum levels of IL-6 in comparison to controls, confirming the existence of systemic inflammation. Elevated serum IL-6 levels were observed as the severity of airflow limitation increased. This was also correlated with a poor quality of life, as evidenced by a lower BMI, a higher modified Medical Research Council Dyspnea Scale, CAT assessment, and a greater frequency of exacerbations in the former year.