THU0113 ANTI CARBAMYLATED PROTEIN ANTIBODY IN INDIAN POPULATION WITH RHEUMATOID ARTHRITIS – A BETTER PREDICTOR OF DISEASE OUTCOME
Authors: L. Sreekumar, M. Cb, M. Pillai, A. T. Ommen, T. C. Vishnu
Journal: Annals of the Rheumatic Diseases (2020)

Background: While diagnosis of RA relies mainly on detection of RF and ACCP antibodies at present, anti carbamylated protein antibody which has strong association with severe joint damage and poorer disease outcome 1 can be found in even healthy individuals years before onset of symptoms of RA 2,3 thus enabling early initiation of DMARDs and reducing complications of RA. 4 Objectives: Assess prevalence of anti-CarP Ab in RA patients in India and assess correlation between joint involvement, X-ray erosions and extra articular features between anti-CarP Ab positive and negative RA patients. Methods: Cross-sectional study (2017-2019) conducted among 150 RA patients who met 2010 ACR/EULAR criteria in tertiary referral hospital. Tests for CRP, RF and ACCP were done, DAS28-CRP scores were calculated at presentation &amp; X-ray images of hands and feet obtained. Anti-CarP Ab was tested using ELISA. Cut-off level for positivity was defined using ROC curve as 13.48 U/mL, with specificity 92.73%, sensitivity 85.26%, PPV 95.29% and NPV 78.46%. Results: Venn diagram representing overlap of sero-markers Study population had 18% males, 82% females, 72% RF+ cases (108), 78% ACCP+ cases (117) and 47.3% anti-CarP Ab+ cases (71). 48% of the 25 seronegative (RF-ACCP-) cases tested positive for anti-CarP Ab, indicating its ability in diagnosing more RA cases in conjunction with present markers. Testing association between RF and anti-CarP Ab and between ACCP and anti-CarP Ab proved to be statistically insignificant showing that anti-CarP Ab is independent of the incumbent markers in diagnosing RA. 69.4% of RA patients with high disease activity (DAS &gt;3.2) were positive for anti-CarP Ab and showed statistically significant association. Association between DAS28 CRP and anti-CarP Ab Also while 39 of 71 (54.9%) anti-CarP Ab positive RA cases had joint deformities and 23 of 71 (32.4%) of anti-CarP Ab positive cases had extra articular involvement and were statistically significant, 27 of 71 anti-CarP Ab positive cases showed joint erosions in X-ray but was not statistically significant. In comparison, only extra articular involvement showed a statistical significance in ACCP positive patients whereas joint deformities and joint erosions on X-rays showed no correlation to ACCP. Joint Deformity Total Χ 2 p value Absent Present anti-CarP antibody Negative 50 29 79 5.009 0.025 63.3% 36.7% 100.0% Positive 32 39 71 45.1% 54.9% 100.0% Total 82 68 150 Extra articular features Total Χ 2 p value Absent Present anti-CarP antibody Negative 68 11 79 7.278 0.007 86.1% 13.9% 100.0% Positive 48 23 71 67.6% 32.4% 100.0% Total 116 34 150 Conclusion: Anti-CarP antibody positivity is indicative of increased disease activity (DAS28-CRP score), joint deformities and extra articular involvement in RA patients. Aside from its presence demonstrated early in the course of RA through other studies, its ability in diagnosing RA cases in otherwise seronegative (RF and ACCP negative) population and the high sensitivity, specificity and diagnostic accuracy exhibited paves the way for its routine use as a diagnostic tool in conjunction with RF and ACCP for diagnosing RA and predicting disease outcome. References: [1]Shi J et al. Autoantibodies recognizing carbamylated proteins are present in sera of patients with rheumatoid arthritis and predict joint damage. Proc Natl Acad Sci USA . 2011;108(42):17372-17377. [2]Challener GJ et al. Anti-carbamylated Protein Antibody Levels Correlate with Anti-Sa Antibody Levels in Rheumatoid Arthritis. J Rheumatol . 2016;43(2):273-281. [3]Brink M et al. Anti-carbamylated protein antibodies in the pre-symptomatic phase of rheumatoid arthritis, their relationship with multiple anti-citrulline peptide antibodies and association with radiological damage. Arthritis Research &amp; Therapy . 2015;17(1):25. [4]Guidelines for the management of rheumatoid arthritis. American College of Rheumatology Ad Hoc Committee on Clinical Guidelines. Arthritis Rheum . 1996;39(5):713-722. Disclosure of Interests: None declared