Abstract
Classification of patients with rheumatoid arthritis (RA) as quickly as possible improves their prognosis. This reason motivates specially dedicated early arthritis (EA) clinics. Here, we have used 1062 EA patients with two years of follow-up to explore the value of anti-carbamylated protein (anti-CarP) antibodies, a new type of RA specific autoantibodies, for classification. Specifically, we aimed to determine whether the addition of anti-CarP antibodies to IgM rheumatoid factor (RF) and anti-cyclic citrullinated peptide (anti-CCP) antibodies, which are helpful in RA classification, improves it or not. Our analysis showed that incorporation of the anti-CarP antibodies to combinations of the other two antibodies (all joint by the OR Boolean operator) produces a modest increase in sensitivity (2.2% higher), at the cost of decreased specificity (8.1% lower). The cost-benefit ratio was more favorable in the patients lacking the other autoantibodies. However, it did not improve by considering different titer levels of the anti-CarP antibodies, or after exhaustively exploring other antibody combinations. Therefore, the place in RA classification of these antibodies is questionable in the context of current treatments and biomarkers. This conclusion does not exclude their potential value for stratifying patients in joint damage, disease activity, disability, or mortality categories.
Highlights
The remaining patients showed a variety of diseases, including undifferentiated arthritis (UA) as the most common (20%), and other less common diseases as spondyloarthritis, Sjögren syndrome, systemic lupus erythematosus, psoriatic arthritis, inflammatory bowel disease ..., which jointly added to 30.1% of the total and were considered as the other early arthritis (EA) group (OEA)
Frequencies of the rheumatoid arthritis (RA) antibodies were disparate in RA and non-RA patients, with the anti-CCP antibodies as the most different, followed by rheumatoid factor (RF) and the anti-CarP antibodies in this order (Table 1)
It is worth to note that the anti-CarP titers among the positives were not different between the three groups of patients
Summary
Autoantibodies, the anti-carbamylated protein (anti-CarP) antibodies, could contribute to the early classification of patients with RA and no study has yet done this specific analysis. We do not know yet the proteins that are targeted in patients In their place, the antibodies are assayed against in vitro carbamylated fetal calf serum (FCS)[12,13,14,15]. The anti-CarP antibodies are associated with bone erosions, disease activity, disability and mortality in RA with independence of the anti-CCP antibodies[12, 16,17,18,19] All these characteristics indicate that the anti-CarP antibodies could add to the classification of RA patients. This should be possible by a combination of two factors: the use as classification outcome the 1987 criteria to avoid bias in the assessment of the anti-CarP antibodies relative to RF and the anti-CCP antibodies[7]; and adoption of analysis focused in the improvement of current classification criteria (considering RF or anti-CCP antibodies)[2]
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