Influence of anti-carbamylated protein antibodies on disease activity and joint erosions in seronegative and seropositive rheumatoid arthritis

Anti-carbamylated protein (anti-CarP) antibodies are promising biomarkers in rheumatoid arthritis (RA), although their significance in seronegative disease (SNRA) remains uncertain. To assess the influence of anti-CarP antibodies on disease activity and erosive joint damage in SNRA patients. In RA patients, rheumatoid factor (RF), anti-citrullinated protein antibodies, and anti-CarP antibodies were measured. Disease activity was assessed using DAS28-CRP and SDAI indices, while musculoskeletal ultrasound identified bone erosions. A total of 77 patients were enrolled, comprising 49 with seropositive RA (SPRA) and 28 with SNRA. Notably, 28% of SPRA and 10% of SNRA patients were positive to anti-CarP antibodies. Anti-CarP-positive patients exhibited elevated C-reactive protein (median 10.6, interquartile range 4.6–20.0 vs. 3.4, 1.7–9.9 mg/L; p = 0.005), erythrocyte sedimentation rate (34, 19–46 vs. 16, 7–25 mm/h; p = 0.002), DAS28-CRP (3.2, 2.6–4.2 vs. 2.6, 1.9–3.5; p = 0.048), and SDAI (19.9, 6.3–32.1 vs. 10.9, 5.5–18.1; p = 0.034) indices. Multivariate analysis revealed RF positivity as the sole predictor for anti-CarP antibodies (odds ratio [OR] = 5.9). Musculoskeletal ultrasound revealed bone erosions in 36% of RA patients; 35% among anti-CarP-negative patients and 40% among anti-CarP-positive patients. Notably, RF presence (OR = 44.3) and DAS28-CRP index (OR = 2.4) emerged as predictors of musculoskeletal ultrasound-confirmed erosive joint disease. Anti-CarP antibodies are detected at similar frequencies among both SPRA and SNRA patients. While associated with increased disease activity, these antibodies did not correlate with increased erosive joint damage.