Serum cartilage oligomeric matrix protein (COMP) levels in knee osteoarthritis in a Brazilian population: clinical and radiological correlation.

OBJECTIVES: In this study we present data on serum cartilage oligomeric matrix protein (COMP) levels in a Brazilian population with isolated knee osteoarthritis (OA) compared to healthy controls. Clinical and radiological correlations with COMP levels were also evaluated.
METHODS: Two hundred and seventy-two patients seen at the Rheumatology Division of the Federal University of São Paulo (UNIFESP) with a symptom of 'pain in the knees' for at least 3 months were invited to participate in this study. History and clinical examination were performed in all patients. Eighty-six patients with clinical isolated knee OA according to the American College of Rheumatology (ACR) criteria and without other causes of pain in the knee were included. Fifty-eight healthy individuals were selected, matched for age and sex, and used as controls. OA evaluation included Lequesne and Western Ontario and MacMaster Universities osteoarthritis index (WOMAC) questionnaires, visual analogue scale (VAS) for pain and standard knee X-rays. Blood samples were taken from all participants and serum COMP levels were measured by enzyme-linked immunosorbent assay (ELISA). OA radiological analysis was performed using the Kellgren and Lawrence (K/L) grading scale.
RESULTS: Patients with symptomatic knee OA presented significantly higher serum COMP levels compared to healthy controls and to those with non-symptomatic narrowing of the articular space (p<0.001). Patients with clinical evidence of knee OA and without radiological abnormalities (K/L grade 0 or 1) had intermediate serum COMP levels, significantly higher than those observed in healthy controls (p<0.03).
CONCLUSIONS: We observed increased serum COMP levels in patients with symptomatic radiological knee OA. High serum COMP levels may also indicate cartilage damage in selected symptomatic patients without significant radiological abnormalities.