Abstract

Rheumatoid Arthritis (RA) is the most common form of chronic inflammatory joint disease. The diagnosis of RA may be a challenge in certain patients where the clinical presentation is equivocal and serum Rheumatoid Factor (RF) is negative. The evaluation of joint damage and the disease activity is usually done by radiological scoring and the assessment of Disease Activity Score (DAS). Cartilage Oligomeric Matrix Protein (COMP) is a pentameric glycoprotein that was initially found in articular cartilage. The serum levels of COMP in a group of Egyptian patients with RA were measured and the diagnostic performance of serum COMP was compared to quantitative serum Rheumatoid Factor (RF) and C-Reactive Protein (CRP) values. The current study included 2 groups: a control group, comprised 20 healthy subjects (16 women and 4 men) aged (mean±SD) 43.0±15.22 years and a patients group, comprised 30 rheumatoid arthritis patients (24 women and 6 men) aged 48.4±12.39 years. Serum COMP was significantly higher in patients with rheumatoid arthritis when compared to the controls (p<0.01). The median range of serum COMP was 7.49 (4.95-9.56) and 8.78(6.41-27.3) U L-1 in controls and patients with rheumatoid arthritis respectively. When patients with RA were classified into a seronegative and a seropositive subgroups, serum COMP showed a superior diagnostic value in seronegative patients compared to quantitative RF. The Area Under the Curve (AUC) for the COMP was 0.771 (p value 0.011 and the 95% Confidence Interval (CI) was 0.602-0.940), while the AUC for the quantitative RF was 0.673 (p value: 0.106 and the 95% CI was 0.465-0.88). Using Youden index the best cutoff value for serum COMP in seronegative patients was 8.9 U L-1, which had a sensitivity of 58%. On the other hand using the same index the best cutoff value for RF was 7.35 IU mL-1, which had a sensitivity of only 42%. When both COMP and quantitative RF were combined, a higher sensitivity of 83% was achieved. The current study has found a significantly elevated serum COMP in Egyptian patients with RA compared to controls. Furthermore serum COMP has a higher diagnostic performance in RA with low serum quantitative RF titer (seronegative patients). When both serum COMP and quantitative RF values were combined a better diagnostic sensitivity was achieved.