Chronic obstructive pulmonary disease (COPD) is a common disease among elderly individuals, affecting more than 600 million people worldwide, and has become the third leading cause of death [1]. Especially in developing countries, the main risk is tobacco smoking, but other environmental exposures, such as air pollution and biomass fuel exposure, may contribute. Although COPD is often defined as the presence of chronic persistent and irreversible airflow limitation, it is considered a complex, heterogeneous disease with multiple comorbidities that may contribute to a wide variety of manifestations. Indeed, COPD and coexisting diseases are interlinked beyond simple coincidence but may influence the occurrence and development of each other through the action of inflammatory mediators throughout the body. Therefore, in-depth knowledge of the underlying correlations of these diseases with inflammatory mediators is necessary.

In particular, many inflammatory markers have been found to be closely associated with common diseases in the elderly. Therefore, we proposed a scientific hypothesis: Is there a close correlation between the occurrence of co-morbidities and inflammation in patients with COPD who have systemic inflammation as the most important manifestation? With the development of medicine, scientists have found some clinically traditional inflammatory indicators, such as red blood cell distribution width (RDW), originally used as a parameter reflecting the degree of erythrocyte heterogeneity, seem to be redefining its clinical role, which has been found in the diagnosis and prediction of pulmonary hypertension [2], cardiovascular disease [3] and inflammation-related diseases [4], [5]. In addition, neutrophil/lymphocyte ratio (NLR), monocyte/lymphocyte ratio (MLR) and platelet/lymphocyte ratio (PLR) were also found to be strongly associated with COPD [6], acute coronary syndrome [7], severe psychiatric disorders [8], and colorectal cancer [9]. Therefore, we would like to find an association between these clinically commonly used, inexpensive, simple and readily available indicators and several common comorbidities in patients with COPD.

In terms of interleukin-6 (IL-6) and interleukin-1β (IL-1β), as important airway inflammatory cytokines, their relationship with COPD has been well elucidated in previous studies [10], [11]. Recent studies have found that IL-1β and IL-6 are closely associated with hypertension [12], diabetes [13] and depression [14], and are considered to be the most reliable inflammatory biomarkers in major depression [15]. To note, depression and anxiety are common in COPD patients whose condition is characterized primarily by inflammation [16], [17], [18]. Although most physicians believe that the progressive deterioration of the condition, the loss of social function, and the unaffordable financial burden, which are the most fundamental causes of depression and anxiety in COPD patients. However, the facts may be much more complicated than we think. Like major depression [15], IL-1β and IL-6 may have a direct pathogenic effect on depression and anxiety in patients with COPD. This may be the answer we want to find in this study.

Despite the widespread recognition that depression and anxiety are detrimental to humans, in this group of people suffering from COPD, the psychological comorbidities often go undiagnosed or undertreated due to the prioritization of treatment for other physical comorbidities. Even at the large tertiary hospital where our study was conducted, COPD patients with depression or anxiety were not receiving any treatment, neither psychiatrist consultations nor antipsychotic medications. So it seems essential to pay attention to this field. Through this study, we hope to arouse the attention of clinicians to the psychological co-morbidities of patients with COPD, so as to improve the treatment strategies of respiratory physicians and reduce the occurrence of co-morbidities.