Anti-CarP Antibodies May Aid in Predicting RA Severity

A new group of autoantibodies known as anti-carbamylated protein (anti-CarP) antibodies, have been identified and may be able to predict disease activity and disability among patients with early inflammatory arthritis.

The presence or absence of autoantibodies provides important prognostic information to clinicians and patients. Two types of autoantibodies, rheumatoid factor (RF) and anti-citrullinated protein antibodies (ACPA) are recognized as being associated with worse disease activity, more disability, and increased mortality among patients with rheumatoid arthritis (RA).

Some patients however, who have neither of these autoantibodies ultimately experience a severe disease course. If these “seronegative” patients could be distinguished from those with a milder disease course, they could potentially benefit from early aggressive intervention. New research suggests that knowledge of anti-CarP antibody status in these patients may be helpful in determining treatment for these patients.

Doctors have previously reported that both disability and disease activity are greater among individuals who tested positive for anti-CarP.1 Dutch doctors have now confirmed these observations among a group of patients with early inflammatory arthritis.2

Among 1,476 patients who underwent testing for autoantibodies, 31% were positive for RF, 26% for ACPA, and 20% for anti-CarP. The only autoantibody detected was anti-CarP in 5%. Individuals with anti-CarP were more disabled at initial evaluation and had higher disease activity persisting over time. The study authors also observed that the effect of each antibody could be considered to be additive in the random effects model.

This analysis suggests that anti-CarP antibodies may be important for predicting long-term outcomes in patients with inflammatory polyarthritis, and may be useful to test in addition to ACPA and RF. Commercial assays for detection of anti-CarP however are currently unavailable and use of the assay is limited to selected centers at this time.
1. Humphreys J, Verheul M, Barton A, et al. Anticarbamylated protein antibodies are associated with long-term disability and increased disease activity in patients with early inflammatory arthritis: results from the norfolk arthritis register [abstract .] Published online Oct. 2015. doi:10.1136/annrheumdis-2015-207326.
2. Shi H, Knevel R, Suwannalai P, van der Linden M, et al. Autoantibodies recognizing carbamylated proteins are present in sera of patients with rheumatoid arthritis and predict joint damage [abstract]. Published online 2011 Oct 10 doi: 10.1073/pnas. 1114465108.