Differential effects of systemic immune inflammation indices on hepatic steatosis and hepatic fibrosis: evidence from NHANES 1999-2018

Background Several studies have demonstrated that systemic immune inflammation index (SII) has a positive relationship with hepatic steatosis. However, it is lack of system evidence for the correlation between SII and hepatic fibrosis. The objective of this study was to evaluate the relationships between SII and hepatic steatosis or hepatic fibrosis. Methods A cross-sectional analysis was performed of 21833 subjects aged over 20 from the National Health and Nutrition Examination Survey (NHANES). Fibrosis-4 index (FIB-4), NAFLD fibrosis score (NFS) and hepamet fibrosis score (HFS) were the indicators for hepatic fibrosis; fatty liver index (FLI), NAFLD liver fat score (LFS) and Framingham steatosis index (FSI) were the indicators for hepatic steatosis. Pearson’s test, generalized linear model (GLM) and restricted cubic splines (RCS) were used to analyze associations of SII with hepatic fibrosis and hepatic steatosis. Results Pearson’s test and GLM revealed that there were negative relationships between SII and hepatic fibrosis (FIB-4, NFS and HFS), while positive relationships between SII and hepatic steatosis (FLI, LFS and FSI). The corresponding β (95%CI) of SII and hepatic fibrosis were − 0.35(-0.46, -0.24), -0.67(-0.71, -0.63) and − 0.10(-0.12, -0.09), respectively. The corresponding β (95%CI) of SII and hepatic steatosis were 6.12(4.75, 7.50), 0.22(0.12, 0.31) and 0.27(0.20, 0.34), respectively. Statistically significant non-linear association were found in SII with hepatic fibrosis and hepatic steatosis in RCS model (all P  < 0.001). Conclusion There was a negative significant association between SII and hepatic fibrosis, while a positive significant association between SII and hepatic steatosis.