Detection and clinical significance of anti-carbamylated protein antibody in serologically negative patients with rheumatoid arthritis

Abstract

Objective To probe into the level and clinical significance of anti-carbamylated protein （CarP） antibody in serologically negative patients with rheumatoid arthritis （RA）. Methods A total of 301 RA patients and 55 healthy controls were recruited. Demographic characteristics and clinical data including serum levels of rheumatoid factor （RF） and anti-cyclic citrullinated peptide （CCP） antibody were collected. Serum levels of IgG anti-CarP antibody were determined by ELISA. Results According to the 95th percentile of the anti-CarP antibody level in 55 healthy controls, the ceiling of normal value was ≤31 U/mL. Among 301 RA patients, the positive rates of RF, anti-CCP antibody and anti-CarP antibody were 74.8% （225/301）, 75.1% （226/301） and 15.9% （48/301）, respectively. The positive rates of anti-CarP antibody were 19.7% （15/76） in RA patients with negative RF and 20.0% （15/75） in RA patients with negative anti-CCP antibody, respectively. In negative-RF RA patients, additional detection of anti-CCP antibody could reduce the percentage of serologically negative RA patients by 39.5% （30/76）. Additional detection of anti-CarP antibody could lower the percentage by 19.7% （15/76）. Additional detection of both anti-CCP antibody and anti-CarP antibody could decrease the percentage by 50.0% （38/76）. In serologically negative RA patients （negative for both RF and anti-CCP antibodies）, additional detection of anti-CarP antibody could lower the percentage of serologically negative RA patients by 17.4% （8/46）. Conclusion Additional detection of anti-CarP antibody has supplementary value for the diagnosis of serologically negative RA which is currently a difficult issue in clinical practice.

Keywords

• |rheumatoid arthritis|anti-carbamylated protein antibody|rheumatoid factor|diagnosis|anti-cyclic citrullinated peptide antibody