Correlation between the systemic immune inflammation index and risk of psoriasis: results from NHANES

The systemic immune inflammation index (SII) is an effective indicator of systemic inflammatory status. As psoriasis patients present with systemic involvement, we assessed whether SII is associated with psoriasis in adults. We used data from the National Health and Nutrition Examination Survey (NHANES) from 2003 to 2006 and 2009 to 2014. The study used a multistage sampling design that nationally represents the US population. The main outcome was the prevalence of psoriasis. SII was calculated as platelet count × neutrophil count/lymphocyte count and transformed into log2SII. Sampling weights were calculated according to the guidelines of NHANES. The cohort consisted of 13,300 participants, aged 20-59, who provided responses to their psoriasis status. Among the adults included in this study were 358 with psoriasis and 12,942 without psoriasis. Based on multivariate analysis adjusted for multiple covariates, the highest quartile of log2SII positively correlated with psoriasis relative to the lowest quartile. The subgroup analyses showed that participants in quartile 4 correlated with an increased risk of psoriasis among those aged 40 to 59 years, and among those with obesity or metabolic syndrome. Based on sensitivity analyses, the association between log2SII and psoriasis remained after excluding potential systemic medication use. Based on this cross-sectional study, SII was shown to be associated with psoriasis in the US adult population. Longitudinal monitoring of systemic inflammatory status in psoriasis patients may be necessary to prevent the recurrence of psoriasis, especially for those with obesity or metabolic syndrome.