Serum cartilage oligomeric matrix protein reflects the presence of clinically diagnosed synovitis in patients with knee osteoarthritis

Objective: Cartilage oligomeric matrix protein (COMP) is a component of art icular cartilage whose serum levels show a strong correlation with radiogra phic osteoarthritis (OA) status. It has recently been found, however, that COMP is also produced in synovium. To assess the hypothesis that synovitis affects serum COMP levels in patients with knee OA, we collected sera for C OMP simultaneous with a clinical examination for synovitis. Design: Sera were collected from OA patients who fulfilled the American Col lege of Rheumatology criteria for knee OA. Radiographs were classified acco rding to the grading system of Kellgren and Lawrence. Synovitis was diagnos ed clinically by joint tenderness plus swelling and/or increased warmth ove r the joint. COMP levels in sera were measured by inhibition ELISA with mon oclonal antibody (mAb) 17-C10. Results: Serum COMP levels were significantly correlated with age, synoviti s and an interaction of synovitis and OA severity. Synovitis showed the str ongest effect on COMP levels (R=0.1587, P <0.01), in contrast to C-reactive protein, duration of OA and OA severity score which showed no significant effect on COMP levels. Individual signs of synovitis, namely, joint tendern ess and warmth had a significant effect on serum COMP levels while swelling alone did not. Conclusion: Synovitis exerts a significant effect on serum COMP levels meas ured with mAb 17-C10 in OA patients. These findings underscore the importan ce of the clinical joint examination to assess for synovitis, when attempti ng to apply objective measures, such as COMP, to the clinical setting. (C) 2001 OsteoArthritis Research Society International.