This study investigated the clinical characteristics of red blood cell distribution width (RDW) in rheumatoid arthritis (RA) and the impact of treatment, including longitudinal dose changes. Among 691 RA patients enrolled in 2025, 591 with RDW recorded in both 2024 and 2025 were analyzed. Based on 2024 data, patients were classified into normal RDW (≤14.5%, n = 436) and high RDW (>14.5%, n = 155) groups. Logistic regression identified factors associated with high RDW. Associations with methotrexate (MTX) and glucocorticoid (GC) dose were examined, and one-year changes in RDW (ΔRDW, 2024–2025) were evaluated according to dose modifications. Patients with high RDW were older (70.6 vs 68.0 years), frequently used MTX (71.0% vs 57.6%) and GCs (41.3% vs 18.8%), had higher Disease Activity Score in 28 joints based on erythrocyte sedimentation rate (DAS28-ESR, 2.92 vs 2.68) and Health Assessment Questionnaire Disability Index (HAQ-DI, 0.64 vs 0.40), and lower hemoglobin (11.8 vs 12.9 g/dL). Multivariable analysis revealed that low hemoglobin (odds ratio OR, 0.56), MTX use (OR, 2.47), and GC use (OR, 2.21) were independently associated with high RDW. The prevalence of high RDW increased with higher MTX (14.0%, 18.3%, 28.6%) and GC (14.0%, 20.7%, 43.2%) doses. Longitudinally, ΔRDW rose with MTX initiation or escalation (0.43 ± 0.91 vs −0.08 ± 1.06 or −0.26 ± 1.18), whereas GC changes were not significant. These findings indicate that RDW in RA is influenced more by treatment—particularly MTX use and dose escalation—than by inflammation. GC use also showed cross-sectional associations, though longitudinal effects were less evident. RDW should be interpreted in light of treatment rather than as a simple marker of disease activity.
Ohashi et al. (2026) studied this question.