Urinary total superoxide dismutase activity is low in rheumatoid patients, and its low levels are associated with higher DAS28 scores

Rheumatoid factor and anti-citrullinated peptide antibodies are generally used to diagnose rheumatoid arthritis (RA). However, these antibodies are negative in 15-20 % of RA cases. This study aimed to investigate new biomarkers that can be used in diagnosing RA and evaluating disease activity. Methods: This study included 99 RA patients and 94 healthy volunteers. Modified Disease Activity Score28 (DAS28) erythrocyte sedimentation rate (ESR) was used for disease activity score. Thiol/disulfide molecules were measured using an automatic spectrophotometric method, and ischemia-modified albumin was measured using an albumin-cobalt binding test. A spectrophotometer calculated urinary and serum total superoxide dismutase (SOD) activities at 420 nm wavelength. Results: In the RA group, serum IMA level was higher (unstandardized beta [B]: 5.552, Odds Ratio [OR]: 250.1, CI 95 %: 1.29-48219.1, p: .040), and urinary total SOD activities were significantly lower (B: 2.640 OR: .071, CI 95 %: .027-.192, p < 0.0001) than in the control group. A cut-off value of 5.06 for urinary total SOD was found to have a sensitivity of 97.9 % and a specificity of 97 % in distinguishing RA patients from healthy controls (AUC [95 %Cl] = .986 [.967-1.000], p < 0.001). Urinary total SOD activity was significantly lower in the RA subgroup with high disease activity compared to the groups with moderate disease activity (B: .954, OR: 2.596, CI 95 %: 1.104-6.103, p: .029) and low disease activity (B: 1.251, OR: 3.494, CI 95 %: 1.143-10.678, p: .028). Conclusion: This study showed that urinary total SOD activity has high sensitivity and specificity in distinguishing RA patients from healthy controls and that RA patients with higher DAS28 ESR activity scores have lower urinary total SOD activity.