The specificity of anti-carbamylated protein antibodies for rheumatoid arthritis in a setting of early arthritis.

Jing Shi,E W Nivine Levarht,Tom W J Huizinga,Hanna W Van Steenbergen,Jessica A B Van Nies,Leendert A Trouw,René E M Toes,Annette H M Van Der Helm-Van Mil

doi:10.1186/s13075-015-0860-6

Abstract

IntroductionAnti-carbamylated protein (anti-CarP) antibodies have been described in rheumatoid arthritis (RA) and arthralgia patients at risk of developing RA. To what extent these autoantibodies are specific for RA is unknown. Therefore, we investigated the diagnostic performance of the presence of anti-CarP antibodies for RA in a setting of early arthritis.MethodsAnti-CarP antibodies were detected using carbamylated fetal calf serum as substrate. Anti-CCP2 antibodies were measured using enzyme-linked immunosorbent assay and immunoglobulin M (IgM) rheumatoid factor (RF) as part of routine care. Sera were derived from patients in the Leiden Early Arthritis Clinic cohort obtained at inclusion. Test characteristics were determined using the fulfillment of the 2010 RA criteria after 1 year as outcome.ResultsIn total 2086 early arthritis patients were studied regarding the presence of anti-CarP antibodies. We observed that the sensitivity and specificity of the presence of anti-CarP antibodies for RA were 44 % and 89 %, respectively. As a reference, sensitivity and specificity of the presence of anti-CCP2 antibodies were 54 % and 96 %, respectively, and of IgM-RF 59 % and 91 %. Patients harboring anti-CarP antibodies not classified as RA were mainly diagnosed with undifferentiated arthritis and less frequently reactive arthritis and psoriatic arthritis.ConclusionAnti-CarP antibodies are predominantly present in RA but can also be detected in other forms of arthritis.

Highlights

Anti-carbamylated protein antibodies have been described in rheumatoid arthritis (RA) and arthralgia patients at risk of developing RA
The sensitivity, specificity, positive predictive value, negative predictive value, positive likelihood ratio (LR+) and negative likelihood ratio (LR–) of anti-CarP antibodies for RA were calculated
Sensitivity and specificity of anti-CarP antibodies for RA The Leiden Early Arthritis Clinic (EAC) cohort comprises patients with several forms of recent-onset arthritis which can be encountered in the setting of an outpatient clinic [14]

Summary

Introduction

Anti-carbamylated protein (anti-CarP) antibodies have been described in rheumatoid arthritis (RA) and arthralgia patients at risk of developing RA. To what extent these autoantibodies are specific for RA is unknown. RA can be classified using the 2010 American College of Rheumatology/ European League Against Rheumatism classification criteria (2010 ACR/EULAR criteria) for RA [1]. In this quantitative system points can be obtained from: joint involvement, autoantibodies, acute phase reactants and duration of symptoms [1]. The sensitivity of ACPA (~67 %) for RA is comparable to

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Conclusion