ARTHRITIS & RHEUMATISM Vol. 48, No. 3, March 2003, pp 675–681 DOI 10.1002/art.10822 © 2003, American College of Rheumatology Ethnic and Sex Differences in Serum Levels of Cartilage Oligomeric Matrix Protein The Johnston County Osteoarthritis Project Joanne M. Jordan, 1 Gheorghe Luta, 1 Thomas Stabler, 2 Jordan B. Renner, 1 Anca D. Dragomir, 1 Vladimir Vilim, 3 Marc C. Hochberg, 4 Charles G. Helmick, 5 and Virginia B. Kraus 2 Objective. Previous descriptions of potential bio- markers of osteoarthritis (OA) have been limited to Caucasians. In the present study, we examined associ- ations between serum levels of cartilage oligomeric matrix protein (COMP) and ethnicity (African Ameri- can or Caucasian) and sex in the Johnston County Osteoarthritis Project, a population-based study of OA in rural North Carolina. Methods. All African Americans and a randomly selected sample of Caucasians who had available sera and either no radiographic evidence of knee or hip OA according to the Kellgren/Lawrence (K/L) system (K/L grade 0) or radiographic evidence of knee OA (K/L grade 2 or higher) were included. Serum COMP levels were quantified by sandwich enzyme-linked immunosor- bent assay, using monoclonal antibodies 16-F12 and 17-C10. Linear regression models were used to assess relationships between serum levels of natural log– transformed COMP (ln COMP) and ethnicity and sex, controlling for age, height, body mass index (BMI), radiographic OA, and the presence of other symptom- atic joints. Radiographic OA was defined in separate models as the presence, severity, and laterality of radio- graphic knee OA, the co-occurrence of radiographic knee and hip OA, and the number of knees and hips with radiographic OA. Results. The 769 subjects in the study sample had a mean  SD age of 62  10.3 years. Levels of ln COMP were associated with age, BMI, and all definitions of radiographic OA (P  0.0001), and varied by ethnicity and sex. In adjusted models, ln COMP was higher in African American women than in Caucasian women (P  0.003) and higher in Caucasian men than Cauca- sian women (P  0.0001). There were no statistically significant differences in serum ln COMP levels be- tween African American men and women. Conclusion. Serum COMP levels vary by ethnicity and sex. These factors should be considered in the derivation of standards using this, and possibly other, potential biomarkers of OA. Cartilage oligomeric matrix protein (COMP) is a 524-kd pentameric glycoprotein that is found predomi- nantly in cartilage, but is also present in ligament, tendon, meniscus, and synovium (1–3). Elevated serum levels of COMP have been found in persons with knee osteoarthritis (OA) compared with healthy individuals (2), in persons with OA-related type II collagen gene mutations (4), in those with knee OA with synovitis compared with those with knee OA without synovitis (3), and in those with systemic inflammatory arthropathy due to rheumatoid arthritis (5,6). Using monoclonal antibody 17-C10 in an inhibition enzyme-linked immu- Drs. Jordan, Luta, Renner, and Dragomir’s work was sup- ported by grant S043 from the CDC/Association of Schools of Public Health and by Multipurpose Arthritis and Musculoskeletal Diseases Center grant 5-P60-AR-30701 from the National Institute of Arthritis and Musculoskeletal and Skin Diseases. Drs. Stabler and Kraus’ work was supported by a Biomedical Science grant from the Arthritis Foundation, by grant AG-15108 from the NIH, and by National Institute on Aging grant 5-P60-AG-11268 from the NIH. Dr. Vilim’s work was supported by grant NK/6813-3 from the Internal Grant Agency of the Ministry of Health, Czech Republic. 1 Joanne M. Jordan, MD, MPH, Gheorghe Luta, MS, Jordan B. Renner, MD, Anca D. Dragomir: University of North Carolina, Chapel Hill; 2 Thomas Stabler, BS, Virginia B. Kraus, MD, PhD: Duke University Medical Center, Durham, North Carolina; 3 Vladimir Vilim, PhD: Institute of Rheumatology, Prague, Czech Republic; 4 Marc C. Hochberg, MD, MPH: University of Maryland, Baltimore; 5 Charles G. Helmick, MD: Centers for Disease Control and Prevention, Atlanta, Georgia. Address correspondence and reprint requests to Joanne M. Jordan, MD, MPH, Thurston Arthritis Research Center, 3310 Doc J. Thurston, Jr. Building, CB#7330, University of North Carolina, Chapel Hill, NC 27599-7330. Submitted for publication June 18, 2002; accepted in revised form November 18, 2002. 675