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Study: High SII Linked With Increased Respiratory Failure, Death Risk in Patients With COPD


The systemic immune-inflammation index (SII) was found to be a potential predictor of the prognosis of patients with chronic obstructive pulmonary disease (COPD).

High systemic immune-inflammation index (SII) is closely linked to an elevated risk of respiratory failure (RF) and death in patients with chronic obstructive pulmonary disease (COPD), according to a study published in the International Journal of Chronic Obstructive Pulmonary Disease.

The researchers explained that RF, especially hypercapnic RF (HRF) frequently occurs in patients with severe or end-stage COPD; COPD complicated by RF (COPD+RF) increases the difficulty of treatment, resulting in poor prognosis and unplanned hospitalization. Due to the negative influence COPD+RF has on patients’ health and quality of life, the researchers claimed that early RF risk identification in patients with COPD is important to implement preventative strategies as early as possible. To do so, they need an easily accessible biomarker related to RF incidence to predict patients’ clinical outcomes.

The researchers noted that one potentially useful biomarker could be SII, “a comprehensive inflammatory indicator that is computed by peripheral lymphocyte, neutrophil, and platelet counts.” They explained that SII is regarded as a powerful inflammatory indicator of both local immune response and systemic inflammation, and it has been indicative of poor prognosis or stroke, cardiovascular diseases, acute kidney injury, and sepsis. However, no study has been conducted to understand how SII influences the prognosis of critically ill patients with COPD.

Therefore, the researchers conducted a study to analyze the relationship between SII and the risk of RF and death in critically ill patients with COPD; it also assessed the prognostic value of SII in this population, guiding the prevention and treatment of COPD+RF. More specifically, the primary outcome analyzed was the incidence of RF, and the secondary outcomes investigated were in-hospital all-cause mortality and mortality during long-term follow-up.

flat lining patient in hospital | Image Credit: kinomaster - stock.adobe.com

The systemic immune-inflammation index (SII) appears to be a potential predictor of the prognosis of patients with chronic obstructive pulmonary disease (COPD). | Image Credit: peterschreiber.media - stock.adobe.com

To do so, the researchers retrospectively acquired relevant data from the Medical Information Mart for Intensive Care-IV (MIMIC-IV), a sizable, open-access database that includes the clinical data of 299,712 patients hospitalized in the Beth Israel Deaconess Medical Center (BIDMC) from 2008 to 2019.

They included adult patients diagnosed with COPD according to the ninth and 10th revisions of the International Classification of Diseases (ICD-9, ICD-10). Conversely, the researchers excluded patients who had RF at admission, patients hospitalized for less than 24 hours, and patients whose platelet, lymphocyte, and neutrophil counts were missing or 0.

Initially, the researchers retrospectively extracted 14,050 patients with COPD from the MIMIC-IV database, but they ultimately analyzed 1653; the study population consisted of 879 (53.2%) males and 774 (46.8%) females. The study population's average age was 71.0 years (range, 62.0-78.0 years), and the average SII was 1302.17 (range, 634.51-2821.88). The researchers noted that patients with a high SII were mostly older White males with more unstable vital signs and higher disease scores at admission.

Additionally, RF occurred in 697 (42.2%) patients, and HRF occurred in 427 (25.8%) patients. Also, 169 patients died in the hospital, with 130 (7.9%) deaths in the intensive care unit (ICU) and 39 (2.3%) deaths during hospitalization; the researchers determined that 637 (38.5%) patients died during follow-up. Lastly, they explained that the median follow-up time for RF, in-hospital death, and follow-up death was 5.0 (range, 1.0-9.0), 8.0 (range, 5.0-15.0), and 29.0 (range, 8.0-187.0) days, respectively.

Overall, the researchers determined that SII is linked to an elevated risk of RF and death in patients with COPD. Their findings showed that higher SII increased patients’ risk of RF (HR, 1.19; 95% CI, 1.12-1.28; P < .001), in-hospital mortality (HR, 1.22; 95% CI, 1.07-1.39; P = .003), and long-term follow-up mortality (HR, 1.12; 95% CI, 1.05-1.19; P < .001). More specifically, a Kaplan-Meier analysis suggested a significantly elevated risk of all-cause death (log-rank P < .001) in patients with higher SII, especially during the short-term follow-up period of 21 days.

The researchers acknowledged their study’s limitations, one being that it has a single-center retrospective design. Therefore, the study population was subject to selection bias, resulting in the limited generalizability of their findings to other populations. Despite its limitations, the researchers expressed confidence in their findings, making future research suggestions based on them.

“…SII serves as a potential, cost-effective, and easily available biomarker for early risk assessment of this population,” the authors concluded. “Nevertheless, larger prospective studies with long-term follow-up are desired to corroborate our conclusions.”


Zhang Y, Tan X, Hu S, Cui Z, Chen W. Relationship between systemic immune-inflammation index and risk of respiratory failure and death in COPD: a retrospective cohort study based on the MIMIC-IV database. Int J Chron Obstruct Pulmon Dis. 2024;19:459-473

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