Diagnostic value of anti-Sa antibody and anti-carbamylated protein antibody for rheumatoid arthritis

Abstract

Objective: To investigate the diagnostic value of anti-Sa antibody and anti-carbonylated protein (CarP) antibody for rheumatoid arthritis (RA). Methods: A retrospective selection of 180 patients with RA who came to Qinghai Provincial People's Hospital from September 2022 to February 2023. Grouped according to the Disease Activity Score of 28 joints (DAS28), 101 of them were patients with RA in high activity (RAH group), 24 males and 77 females, aged 18-79 (53.2±12.2), and 79 patients with RA in low activity (RAL group), 23 males and 56 females, aged 24-78 (49.0±12.9).A total of 90 patients with other autoimmune diseases in the hospital in the same period were choosed as the other immune disease group, and 90 healthy physical examiners were as the healthy control group. The levels of serum anti-Sa and anti-CarP antibodies were measured by ELISA, RF by immunoscattering turbidimetry, anti-CCP by chemiluminescence, and ESR by Weil's method in four groups of patients. The area under the subject operating characteristic (ROC) curve (AUC) was applied to assess the sensitivity and specificity of each index alone or in combination for the diagnosis of RA. Results: In the RAH group, RAL group, other immune disease group, and healthy control group, the RF levels were 117.6 (61.0, 161.1), 92.7 (48.1, 92.7), 10.1 (5.3, 24.6), and 8.1 (6.0, 12.8) U/ml, anti-CCP antibody levels were 202.7 (67.1, 594.4), 212.9 (98.3, 416.2), 9.4 (6.6, 11.8), 1.9 (0.8, 4.9) U/ml, anti-Sa antibody levels were 305.3 (120.4, 614.9), 235.8 (161.6, 336.9), 123.9 (41.8, 240.5), 165.1 (71.1, 237.5) U/ml, and anti-CarP antibody levels were 11.7 (7.9, 21.6), 5.2 (3.3, 7.7), 5.1 (3.9, 6.5), and 5.8 (3.8, 7.5) mg/L, respectively, and their differences were statistically significant (all P<0.001). The level of anti-CarP antibody was higher in the RAH group than in the RAL group (P<0.001), and the difference in anti-Sa antibody was not statistically significant (P>0.05). The critical value of anti-Sa antibody at 181.45 μg/L showed a sensitivity of 67.2%, specificity of 65.6% and AUC of 0.710 (95%CI: 0.645-0.775); The sensitivity was 52.8% and the specificity was 88.9% with an AUC of 0.706 (95%CI: 0.646-0.766) at a critical value of 7.98 U/ml for the anti-CarP antibody. The AUC for the combined RF, anti-CCP antibody and anti-CarP antibody assay was 0.986 (95%CI: 0.977-0.996). Conclusion: Anti-CarP antibody is clinically significant in distinguishing active RA. RF, anti-CCP, and anti-CarP antibodies can be detected together with high AUC results, suggesting the potential for developing an improved method for diagnosing RA.