Interleukin-6 as a Biomarker for Rheumatoid Arthritis-Associated Interstitial Lung Disease: A Retrospective Study

This study aims to assess the predictive value of interleukin-6 (IL-6) as a biomarker in patients with rheumatoid arthritis-associated interstitial lung disease (RA-ILD).

A total of 361 RA patients (236 RA non-ILD and 125 RA-ILD patients) are included in the study, and stratified analysis is performed according to age and gender. The RA-ILD group is divided into mild ILD, moderate ILD, and severe ILD groups based on HRCT score. Using logistic regression analysis to investigate the risk association between IL-6 and rheumatoid arthritis-associated interstitial lung disease (RA-ILD), and employing receiver operating characteristic (ROC) to determine the value of IL-6 for distinguishing RA-ILD. Pearson's analysis and linear regression are used to analyze the association between IL-6 and RA disease activity, High-Resolution Computed Tomography (HRCT) scores, and Krebs Von den Lungen-6 (KL-6).

The level of IL-6 in the RA-ILD group is higher than that in the RA non-ILD group (p < 0.001). The OR of IL-6 associated with the risk of ILD is 1.03 (p < 0.001). IL-6 demonstrated significant diagnostic utility in distinguishing RA-ILD patients from RA patients without ILD, with an area under the receiver operating characteristic curve (AUC) of 0.810 (95% CI: 0.767-0.854; p < 0.001). At the best cutoff value of 8.87 pg/mL, IL-6 exhibited a sensitivity of 94.4% and specificity of 63.6%. There is no statistically significant difference in IL-6 among the ILD subgroups (p > 0.05). Pearson correlation analysis and multiple linear regression analysis show that IL-6 is significantly positively correlated with Disease Activity Score-28 (DAS28), but does not significantly correlate with HRCT score and KL-6.

IL-6 may be used as a new peripheral blood biomarker to predict RA-ILD.