Diagnostic value and clinical significance of anti-carbamylated protein (anti-CarP) antibodies in Egyptian patients with rheumatoid arthritis

The study was performed to assess the diagnostic potential of anti-carbamylated proteins (anti-CarP) antibodies in Egyptian patients with RA and their relation to clinical manifestations, laboratory findings and radiological damage. The study involved 90 RA patients and 90 matched healthy controls. Disease activity score (DAS28) and health assessment questionnaire (HAQ) were assessed. Plain x-ray hands and feet were performed and assessed by modified Larsen’s score. Laboratory investigations including acute phase reactants, rheumatoid factor (RF), anti-cyclic citrullinated peptide (anti-CCP) and anti-CarP antibodies were estimated. The patients mean age was 42.6 ± 10.4 years (20–60 years), disease duration was 4.3 ± 3.3 years and were 82 females (91.1%) and 8 males (8.9%). The mean DAS28 was 4.9 ± 1.2, HAQ was 1.6 ± 0.7 and Larsen score 33.8 ± 12.2. 29/90 (32.2%) patients were positive for anti-CarP antibodies and were significantly associated with extra-articular manifestations and deformity (p < 0.001), but not with acute phase reactants. Anti-CarP antibodies significantly associated with modified Larsen’s (p < 0.001), but not DAS28 (p = 0.13). The sensitivity and specificity were 32.2% and 96.7% for anti-CarP antibodies, 61.1% and 97.8% for anti-CCP antibodies, 66.7% and 91.1% for RF respectively. 25.7% of anti-CCP negative patients showed anti-CarP positivity, and radiological damage was significantly associated with anti-CarP in them. The sensitivity of anti-CarP antibodies was low in comparison to both RF and anti-CCP; however, they showed high specificity and were detected in anti-CCP negative patients, so they could be useful to test beside anti-CCP and RF. Anti-CarP antibodies may reflect disease radiological damage.