Background/Purpose

Anti-carbamylated protein (anti-CarP) antibodies have been described in rheumatoid arthritis (RA) and arthralgia patients [1;2] and occur in subsets of the anti-CCP2 positive and negative patients [1;3]. In anti-CCP2 negative RA patients the presence of anti-CarP was associated with more severe joint destruction [1]. Here we investigated the sensitivity and specificity of anti-CarP antibodies for RA in a setting of early arthritis.

Methods

Anti-carbamylated fetal calf serum (anti-Ca-FCS), anti-CCP2 antibodies and rheumatoid factor (RF) IgM were measured by ELISA using serum samples available from a large inception cohort; the Leiden Early Arthritis Clinic cohort (EAC). For the anti-CarP antibodies we used as a cut-off for positivity the mean + 2 times the standard deviation of the healthy controls [1].

Results

In total 2086 sera of Leiden EAC patients suffering from early arthritis were analyzed for the presence of anti-Ca-FCS antibodies. Anti-CarP antibodies were present in 26% of the patients and in 2% of the controls. We observed that the sensitivity and specificity of anti-Ca-FCS in the EAC cohort for RA are 44% and 89%. As a reference the sensitivity and specificity of anti-CCP2 antibodies are 54% and 95% and for RF IgM are 59% and 90%. Analyzing the early arthritis patients that did not fulfil the EULAR/ACR 2010 criteria for RA that were anti-CarP positive (n=127) revealed that these patients were mainly diagnosed as undifferentiated arthritis (45%), reactive arthritis (9%), psoriatic arthritis (9%) or peripheral spondyloarthritis (8%).

Conclusion

Anti-CarP antibodies, as determined by the reactivity to carbamylated FCS, are predominantly present in RA but can also be detected in other forms of arthritis. The prognostic relevance of anti-CarP antibodies in these latter patients will have to be determined.

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.U.S.A 2011; 108:17372-7.

2.    Shi J, van de Stadt LA, et al. Anti Carbamylated Protein Antibodies (anti-CarP) are present in arthralgia patients and predict the development of rheumatoid arthritis. Arthritis Rheum. 2012.

3.    Jiang X, Trouw LA, et al. Anti-CarP antibodies in two large cohorts of patients with rheumatoid arthritis and their relationship to genetic risk factors, cigarette smoking and other autoantibodies. Ann.Rheum.Dis. 2014.

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/the-specificity-of-anti-carbamylated-protein-antibodies-for-rheumatoid-arthritis-in-a-setting-of-early-arthritis/