Association between systemic immune-inflammation index and psoriasis: A cross-sectional study

Abstract Objectives The Systemic Immune-inflammatory Index (SII), an emergent biomarker for inflammation, has recently garnered attention. Psoriasis, characterized by its immune-inflammatory nature, presents an intriguing domain for exploring potential associations with SII. This investigation is poised to unravel the complexities of this relationship. Methods Leveraging data from the National Health and Nutrition Examination Survey (NHANES), spanning five distinct cycles (2003–2004, 2005–2006, 2009–2010, 2011–2012, and 2013–2014), this cross-sectional study meticulously calculated the SII, taking into account lymphocyte, neutrophil, and platelet counts. Questionnaire data from individuals with psoriasis were meticulously analyzed. An array of statistical methodologies was employed to discern the linear and non-linear relationships between SII and psoriasis, including multivariate regression, subgroup analyses, smoothed curve fitting, and threshold effect analyses. Results Encompassing a demographic of 23,825 Americans, this population-based study identified 623 individuals (2.61%) with psoriasis. Following a rigorous adjustment for pivotal covariates such as age, gender, and race, multivariate logistic regression analyses unveiled a significant and positive correlation between SII and psoriasis (OR = 1.14, 95% CI = 1.01–1.29, P = 0.0286), with the interaction test demonstrating robustness in this association. Intriguingly, the relationship between SII and psoriasis was elucidated to be non-linear, as evidenced by a two-stage linear regression model, pinpointing an inflection point at 790.4 (1,000 cells/l). Conclusion The present study establishes an independent association between a self-reported history of psoriasis and SII. Moreover, it delineates SII as an independent risk factor for psoriasis at levels below 790.4 (1,000 cells/l), thereby contributing valuable insights into the immunological landscape of psoriasis.