Determinants of anti-HBs decline in rheumatoid arthritis patients undergoing rituximab therapy

To evaluate longitudinal changes in hepatitis B surface antibody (anti-HBs) titers and determinants of seroprotection among patients with rheumatoid arthritis (RA) receiving Rituximab (RTX). Primary outcomes were titer trajectory and loss of seroprotection (<10 IU/L). Longitudinal change of anti-HBs titers was tested with Friedman and Wilcoxon signed-rank tests; seroprotection proportions with McNemar's test. Associations and predictors were examined using Spearman correlations and multivariable logistic regression (odds ratios [ORs], 95% CIs). Analyses were performed in SPSS 26.0 and cross-validated in Python (SciPy 1.11). Anti-HBs titers declined sharply within 3 months of RTX initiation (mean 463.2→218.3 IU/L; <i>p</i> < .01), continued to fall between 3-6 months (to 170.2 IU/L; <i>p</i> < .05), and then attenuated, approaching a plateau by 12-24 months (128.5→119.3 IU/L; not significant). The overall time effect was significant (Friedman <i>p</i> = .005). The multivariable model (Nagelkerke R² = 0.284; accuracy 76.9%) identified baseline anti-HBs as the strongest independent predictor: each 100-IU/L increase reduced the odds of losing protection by ~35% (OR 0.65, 95% CI 0.48-0.87; <i>p</i> = .004). Higher total IgG was modestly protective (OR 0.72, 95% CI 0.54-0.95; <i>p</i> = .031). Concomitant corticosteroid use showed a non-significant trend toward higher risk (OR 1.94, 95% CI 0.92-4.71; <i>p</i> = .078). RTX therapy in RA causes a significant, time-dependent reduction in serum anti-HBs titers, most prominently within the first three months. Lower baseline antibody titers and steroid use partially were identified as risk factors for loss of protection, whereas higher IgG levels were protective. Clinically, these findings emphasize the need for pre-treatment anti-HBs screening, potential booster vaccination before RTX initiation, and close serological monitoring during the first 3-6 months of therapy.