THU0113 ANTI CARBAMYLATED PROTEIN ANTIBODY IN INDIAN POPULATION WITH RHEUMATOID ARTHRITIS – A BETTER PREDICTOR OF DISEASE OUTCOME

Abstract

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 outcome1can be found in even healthy individuals years before onset of symptoms of RA2,3thus enabling early initiation of DMARDs and reducing complications of RA.4Objectives: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 & 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-markersStudy 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 >3.2) were positive for anti-CarP Ab and showed statistically significant association.Association between DAS28 CRP and anti-CarP AbAlso 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 DeformityTotalΧ2p valueAbsentPresentanti-CarP antibodyNegative5029795.0090.02563.3%36.7%100.0%Positive32397145.1%54.9%100.0%Total8268150Extra articular featuresTotalΧ2p valueAbsentPresentanti-CarP antibodyNegative6811797.2780.00786.1%13.9%100.0%Positive48237167.6%32.4%100.0%Total11634150Conclusion: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.