Systemic Immune-Inflammation Index and Risk of Diabetes and Prediabetes Two Years Post-COVID-19: A Retrospective Cohort Study.

Background: Post-COVID-19 metabolic complications, such as diabetes, are linked to systemic inflammation. The Systemic Immune-Inflammation Index (SII) may help predict these outcomes; however, evidence from non-Western populations remains limited. Methods: In this retrospective cohort study, 2,060 COVID-19 patients hospitalized in 2020 in Iran were followed for two years. SII was calculated and categorized as normal or elevated. The incidence of diabetes and prediabetes was assessed using fasting blood sugar (FBS) and HbA1c levels. Linear regression analyses were conducted to examine associations between SII and metabolic outcomes, adjusting for potential confounders. Results: Among participants, 73.4% remained normoglycemic, 7.5% developed prediabetes, and 19.1% developed diabetes. Linear regression analysis demonstrated a statistically significant but modest positive association between SII and FBS levels (β = 0.018; 95% CI: 0.004-0.032; P = 0.011). Other inflammatory markers showed no significant associations. Conclusion: Elevated SII was modestly associated with higher fasting blood sugar levels two years after COVID-19 infection. Although the effect size was small, these findings suggest that systemic inflammation may play a role in long-term glycemic dysregulation, underscoring the importance of metabolic follow-up in individuals with heightened post-COVID inflammatory profiles.