SERUM YKL-40 LEVELS IN HEALTHY CHILDREN AND ADULTS. COMPARISON WITH SERUM AND SYNOVIAL FLUID LEVELS OF YKL-40 IN PATIENTS WITH OSTEOARTHRITIS OR TRAUMA OF THE KNEE JOINT

YKL-40 is a recently discovered human glycoprotein which isrelated in amino acid sequence to the chitinase protein family.YKL-40 is a major secretory protein of human chondrocytes andsynoviocytes, and could play a role in tissue remodelling. Theaim of the study was to establish the serum YKL-40 level innormal subjects and to evaluate serum YKL-40 as a marker forosteoarthritis. Serum YKL-40 was 80 µg/1 in healthy children(n = 476) and 102 µg/1 in healthy adults (n = 260). Noage or sex differences were found in serum YKL-40 in subjectsyounger than 70 yr, but thereafter serum YKL-40 increased significantly.Patients with late-stage osteoarthritis of the knee (n = 37)had significantly higher serum YKL-40 (1.5-fold; P < 0.01)compared to healthy age-matched subjects, whereas patients withearly-stage osteoarthritis of the knee or recent torn cruciateligaments or menisci did not have elevated serum YKL-40. Thelevel of YKL-40 in serum and synovial fluid correlated significantly,and 10-fold higher values were found in synovial fluid. YKL-40levels in serum and synovial fluid of patients with acute severesynovial inflammation were significantly higher (P < 0.05-P0.001) than those in patients with no, light or moderate synovitisof the knee joint. Furthermore, YKL-40 correlated significantly(P < 0.01) with the amino-terminal propeptide of type IIIprocollagen, but not with serum C-reactive protein. Our dataindicate that YKL-40 in synovial fluid and serum may reflecthuman articular cartilage degradation and the degree of synovialinflammation in the knee joint. KEY WORDS: Osteoarthritis, Biochemical markers