Higher SII Levels Indicate Higher COPD Prevalence, All-Cause Mortality Risk

Higher Systemic Immune-Inflammation Index (SII) levels are linked to a higher prevalence of chronic obstructive respiratory disease (COPD), according to a study published in BMC Pulmonary Medicine.

The researchers explained that the SII “is a multi-marker index that provides a comprehensive measurement of the systemic immune-inflammatory response in the human body” based on lymphocyte, neutrophil, and platelet counts. Elevated SII levels are associated with worse prognosis and higher mortality in patients with cardiovascular disease and cancer.

Indicated by increased neutrophil and platelet counts, and decreased lymphocyte counts, the researchers noted that some studies suggested that SII serves as a chronic inflammation marker. Similarly, they explained that studies demonstrated a connection between inflammation and immunity with COPD onset and progression.

Despite this, there is a lack of large-sample studies on the association between COPD and SII. Consequently, the researchers explored the SII’s correlation with COPD as it bears significant importance for the prevention and treatment of the disease.

The researchers created their study population using the National Health and Nutrition Examination Survey (NHANES), which “utilizes nationally representative samples and multi-stage sampling designs to monitor conditions biennially.” They analyzed data from surveys conducted between 1999 and 2010.

The researchers initially collected data on 35,479 participants, but the final population consisted of 16,636 patients (8325 men [50.042%] and 8311 women [49.958%]) 40 years and older, after excluding those with missing data. The population consisted of Mexican American patients (18.328%), non-Hispanic White patients (53.889%), non-Hispanic Black patients (18.532%), and others (9.251%).

“Logistic regression analysis was performed to assess the correlation between COPD, lung function, chronic respiratory symptoms, and SII,” the authors wrote. “We used Cox proportional hazards (PH) model to analyze the relationship between SII and mortality in patients with COPD and healthy individuals. We used propensity score matching (PSM) method to match the COPD population with similar baseline levels with the normal population to further analyze the correlation between SII and COPD.”

Overall, the study linked higher SII levels to the greater prevalence of COPD. Also, the researchers found that patients with COPD have a higher risk of all-cause mortality.

Through the multivariable logistic regression analysis, the researchers discovered that a higher SII level was independently associated with a greater likelihood of developing COPD (odds ratio [OR], 1.449; 95% CI, 1.252-1.676; P < .0001) after controlling for all other factors. Also, subgroup analyses showed a significant positive correlation between SII and COPD in different age groups, body mass index levels, genders, smoking statuses, and history of hypertension. Additionally, the researchers found that the SII had a positive correlation with COPD after PSM (OR, 1.673; 95% CI, 1.443-1.938).

“After full adjustment, an increase in the SII is associated with a higher all-cause mortality rate,” the authors wrote. In the general population, patients with COPD, and healthy individuals, HRs were 1.161 (95% CI, 1.088-1.239), 1.282 (95% CI, 1.060-1.550), and 1.129 (95% CI, 1.055-1.207), respectively.

Lastly, the researchers found a significant association between the SII and all-cause mortality rates in patients with COPD. They explained that increased SII potentially reflected heightened systemic inflammation and immune activation, which are causes of disease progression and adverse health outcomes. Chronic inflammation indicated by elevated SII may cause organ dysfunction and tissue damage, increasing the risk of mortality.

The researchers acknowledged their study has several limitations, one being that the study population consists only of Americans, meaning the findings cannot be generalized to other populations. Also, they utilized only patients 40 years and older in the study population, excluding young people.

In terms of future research, the researchers encouraged looking into the underlying mechanisms and potential therapeutic implications related to SII, respiratory health, and lung function. They also noted that it should focus on the exact mechanisms by which SII impacts mortality. Consequently, the researchers explained that “prospective studies and randomized trials are needed to validate these associations and explore the therapeutic implications of modulating SII.”

Reference

Ye C, Yuan L, Wu K, et al. Association between systemic immune-inflammation index and chronic obstructive pulmonary disease: a population-based study. BMC Pulm Med. 2023;23:295. doi:10.1186/s12890-023-02583-5