Serum levels of YKL-40 and C reactive protein in patients with hip osteoarthritis and healthy subjects: a cross sectional study

Background-YKL-40 is a 40 kDa glycoprotein secreted by chondrocytes and syn oviocytes. It has been suggested that it is a surrogate marker of synovial inflammation and joint destruction in rheumatoid arthritis (RA) and osteoar thritis (OA) and related to C reactive protein (CRP) serum levels in RA. Objective-To study serum levels of YKL-40 in patients with hip OA and its r elation with CRP. Methods-YKL-40 and CRP were assayed in serum samples from 45 patients (24 w omen, 21 men, mean age 65) with symptomatic OA of the hip and 33 healthy co ntrols. YKL-40 was assayed by immunoassay and CRP by ultrasensitive immunon ephelometry. OA severity was assessed by the measurement of joint space wid th with a computer analysis system of digitised hip radiographs. Statistica l analysis was performed to determine correlations between serum markers an d radiological joint space width. Results-The mean (standard error) YKL-40 level was 90.3 (8.2) ng/ml in pati ents with hip OA and 66.9 (8.2) ng/ml in controls (p=0.03). The mean CRP le vel was 2.93 (3.03) mg/l in OA and 1.40 (1.61) mg/l in controls (p=0.006). The serum levels of YKL-40 and CRP increased with age and were significantl y correlated (Spearman test: r(s)=0.42, p=0.005) in patients but not in con trols. Neither YKL-40 nor CRP correlated with radiographic joint space widt h. Conclusions-Serum YKL-40 was significantly increased in patients with hip O A. The correlation between YKL-40 and CRP suggests that YKL-40 may be a mar ker of joint inflammation in OA. Longitudinal studies are required to asses s the usefulness of YKL-40 in the monitoring of patients with hip OA.