Objectives The systemic inflammation-immune index (SII) is a biomarker for various diseases; however, its relationship with comorbidities in ankylosing spondylitis (AS) remains unclear. This study aimed to investigate the relationship between SII and the comorbidities associated with AS. Method The cross-sectional study collected data from 688 patients treated at a grade A tertiary hospital in Jiangsu Province between 2021 and 2025. The SII was calculated based on platelet, neutrophil, and lymphocyte counts. Logistic regression analyses were performed. The nonlinear relationship between SII and comorbidities was examined using restricted cubic splines, and interactions between groups were identified through the likelihood ratio test. Results A total of 688 patients were included in the study: 233 with comorbidities and 455 without. The average age was 52.0 ± 14.4 years, with 68.8% being male and 31.2% being female. The incidence of comorbidities was 33.9%. After adjusting for certain covariates, a positive correlation between the SII and comorbidities (OR = 1.3, 95% CI [1.03, 1.64], P = 0.025) was observed, indicating independence from other confounding factors. A non-linear relationship was found between SII and the incidence of comorbidities, with a threshold of approximately 458. Subgroup analysis revealed a significant interaction between SII and disease duration/HLA-B27 (P for interaction < 0.05). A significant additive interaction was observed between SII and disease duration of over 10 years (RERI = 2.49, 95% CI [0.46, 4.52]; AP = 0.52, 95% CI [0.25, 0.79]; SI = 2.92, 95% CI [1.09, 7.85]; P = 0.01). A significant multiplicative interaction exists between HLA-B27( +) and high SII (OR = 2.5, P = 0.03). Conclusions A substantial correlation exists between SII and AS comorbidities, indicating its potential as a predictive biomarker. <Table Float="No" ID="Taba"> <tgroup cols="2"> <colspec align="left" colname="c1" colnum="1" /> <colspec align="left" colname="c2" colnum="2" /> <tbody> <row> <entry align="left" nameend="c2" namest="c1"> Key Points • A substantial correlation exists between SII and AS comorbidities. • A non-linear relationship was found between SII and the incidence of comorbidities. • Subgroup analysis revealed a significant interaction between SII and disease duration/HLA-B27. </entry> </row> </tbody> </tgroup> </Table>

Association between systemic inflammation-immune index and comorbidities in patients with ankylosing spondylitis: a cross-sectional study

期刊论文
发表日期：

2026年3月24日

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Jiang Xiao,
Nan Lin,
Zixin Xu,
Yujie Jiang,
Xinyi Wang,
Yan Sang

摘要

Objectives

The systemic inflammation-immune index (SII) is a biomarker for various diseases; however, its relationship with comorbidities in ankylosing spondylitis (AS) remains unclear. This study aimed to investigate the relationship between SII and the comorbidities associated with AS.

Method

The cross-sectional study collected data from 688 patients treated at a grade A tertiary hospital in Jiangsu Province between 2021 and 2025. The SII was calculated based on platelet, neutrophil, and lymphocyte counts. Logistic regression analyses were performed. The nonlinear relationship between SII and comorbidities was examined using restricted cubic splines, and interactions between groups were identified through the likelihood ratio test.

Results

A total of 688 patients were included in the study: 233 with comorbidities and 455 without. The average age was 52.0 ± 14.4 years, with 68.8% being male and 31.2% being female. The incidence of comorbidities was 33.9%. After adjusting for certain covariates, a positive correlation between the SII and comorbidities (OR = 1.3, 95% CI [1.03, 1.64], P = 0.025) was observed, indicating independence from other confounding factors. A non-linear relationship was found between SII and the incidence of comorbidities, with a threshold of approximately 458. Subgroup analysis revealed a significant interaction between SII and disease duration/HLA-B27 (P for interaction < 0.05). A significant additive interaction was observed between SII and disease duration of over 10 years (RERI = 2.49, 95% CI [0.46, 4.52]; AP = 0.52, 95% CI [0.25, 0.79]; SI = 2.92, 95% CI [1.09, 7.85]; P = 0.01). A significant multiplicative interaction exists between HLA-B27( +) and high SII (OR = 2.5, P = 0.03).

Conclusions

A substantial correlation exists between SII and AS comorbidities, indicating its potential as a predictive biomarker.

Key Points

• A substantial correlation exists between SII and AS comorbidities.

• A non-linear relationship was found between SII and the incidence of comorbidities.

• Subgroup analysis revealed a significant interaction between SII and disease duration/HLA-B27.