Persistence of High Systemic Immune-Inflammation Index as a Predictor of In-Hospital Mortality in COVID-19 Patients

The SARS-CoV-2 infection causes an exaggeration in immune cell activity and massive production of cytokines and inflammatory mediators. This is accompanied by severe lymphopenia, thrombosis, and multiorgan mononuclear infiltration, which determine the severity and mortality of COVID-19. The systemic immune-inflammation index (SII), based on the number of neutrophils, lymphocytes, and platelets, reflects ongoing inflammation and immune status. This study aims to assess the value of the persistence of a high SII in predicting in-hospital mortality of COVID-19 patients.

A retrospective cohort observational study was conducted using data from COVID-19 patients between January and December 2021. The high SII cut-off value was determined using receiver operating characteristic (ROC) analysis. Bivariate analysis was used to determine the relationship between in-hospital mortality and the persistence of high SII and other variables, followed by a multivariate logistic regression model analysis to determine the clinical features associated with in-hospital COVID-19 mortality.  Results: There were 310 COVID-19 patients enrolled, with a mortality rate of 30%. The SII cut-off value was 1942.5x10⁹, and the persistence of high SII was associated with hospital mortality. Multivariate analysis revealed that the administration of additional COVID-19 therapies, disease severity, persistence of high SII, and chronic kidney disease were independently associated with in-hospital mortality.

This study represents a significant association between the persistence of high SII as a prognostic factor for COVID-19 mortality.