Nonlinear association between rheumatoid factor and interstitial lung disease risk in patients with rheumatoid arthritis.

BACKGROUND

Patients with rheumatoid arthritis-associated interstitial lung disease (RA-ILD) face a significantly elevated mortality risk. However, the association between rheumatoid factor (RF) and RA-ILD remains unclear. This study aimed to investigate the relationship between RF and RA-ILD risk, with a focus on potential nonlinear associations and threshold effects.

METHODS

A single-center retrospective cohort of 4,736 rheumatoid arthritis (RA) patients (January 2014-December 2024) was analyzed. Propensity score matching (PSM, 1:1) was applied to control for confounding factors. Multivariate logistic regression and restricted cubic spline (RCS) models were used to evaluate the association between RF levels and RA-ILD risk.

RESULTS

After PSM, 1,018 patients (509 RA-ILD and 509 non-ILD) were included. Multivariate analysis confirmed RF positivity as an independent risk factor for RA-ILD (adjusted OR = 1.506, 95% CI: 1.101-2.061, P = 0.010). A significant nonlinear relationship was observed (P < 0.0001), with a risk threshold identified at 60 IU/mL.

CONCLUSION

RF positivity is an independent risk factor for RA-ILD, demonstrating a nonlinear threshold effect. Clinical practice should emphasize regular RF monitoring and enhanced ILD screening and follow-up, particularly for patients with persistently elevated RF levels. Key Points • RF Positivity is an Independent Risk Factor for RA-ILD. • Paradoxical Risk Reduction at Extremely High RF Levels.