Higher prevalence of chronic obstructive pulmonary disease (COPD) is linked with higher systemic immune-inflammation index (SII) levels; moreover, higher SII levels in patients with COPD are associated with a higher risk for all-cause mortality, according to study findings published in BMC Pulmonary Medicine.

The systemic immune-inflammation index is a quantitative measurement of the systemic immune-inflammatory response in the human body based on lymphocyte, neutrophil, and platelet counts. This index was established as a prognostic indicator for cancer, sepsis, and critical illness. Investigators for the current study sought to assess the correlation between SII and COPD.

The researchers conducted an observational, cross-sectional study that included more than 16,000 participants in the National Health and Nutrition Examination Survey (NHANES; a continuous survey of the nutritional status of noninstitutionalized individuals in the US). The current analysis used data from surveys conducted between 1999 and 2010 and included participants at least 40 years of age, with an even number of women and men. Overall, by ethnicity, 18% were of Mexican heritage, 19% non-Hispanic Black, and 54% non-Hispanic White.

In the current study, diagnosis of COPD was determined based on patients having a ratio of forced expiratory volume in 1 second to forced vital capacity (FEV1/FVC) of less than 0.7 after bronchodilator administration, as well as by self-reported questionnaire answers and patients’ use of COPD treatment-related drugs. Mortality data was gathered from the National Death Index through December 2019.

Increased SII may reflect a heightened state of systemic inflammation and immune activation, which are crucial drivers of disease progression and adverse health outcomes.

Participants with COPD (n=1054) had significantly higher SII scores and were significantly different demographically from participants without COPD (n=15,582) in that they were older, were more often non-Hispanic White, smoked cigarettes, and had a history of diabetes mellitus, hypertension, and cardiovascular disease. The COPD group also included a significantly lower proportion of individuals of Mexican heritage and individuals who had never smoked.

The investigators noted that a higher SII level was independently associated with a higher likelihood of COPD (odds ratio [OR], 1.449; 95% CI, 1.252-1.676; P <.0001) in multivariable logistic regression analysis after controlling for other factors. A significant positive correlation was found between SII and COPD in subgroup analysis of sex, age groups, smoking status, body mass index, and history of hypertension.

After propensity score matching, the investigators noted a positive correlation between the SII and COPD (OR, 1.673; 95% CI, 1.443-1.938). The investigators stated that after full adjustment, an increase in the SII was associated with a higher all-cause mortality rate in the general population (hazard ratio [HR], 1.161; 95% CI, 1.088-1.239), in patients with COPD (HR, 1.282; 95% CI, 1.060-1.550), and in healthy individuals (HR, 1.129; 95% CI, 1.055-1.207).

Study limitations include the use of a US sample population, which limits the study’s generalizability; the exclusion of young adults and adolescents; and an inability to determine causality due to the study’s cross-sectional design.

“Higher SII levels are linked to higher prevalence of COPD,” the investigators concluded, and added, “COPD patients with higher SII levels have a higher risk of all-cause mortality.” The study authors further noted that “Increased SII may reflect a heightened state of systemic inflammation and immune activation, which are crucial drivers of disease progression and adverse health outcomes.”

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