To clarify the significance of YKL-40, also called human cartilage glycoprotein-39, in the serum of patients with RA, we studied serum YKL-40 in relation to clinical and laboratory parameters.
Seventy-two patients (16 men and 56 women) with RA and 40 age-matched healthy persons (14 men, 26 women) were included in this study. Serum levels of YKL-40, insulin-like growth factor-I (IGF-I) and interleukin-6 (IL-6) were measured by ELISA. Radiological changes reflecting joint destruction and the joint score for pain or swelling were assessed by taking into account the joint surface area. Serum CRP levels and the functional disability of patients were also determined.
YKL-40 levels in the serum of patients with RA were significantly higher than those of controls (p < 0.0001), and showed positive correlations with serum levels of IL-6 (r = 0.301, p = 0.011) and CRP (r = 0.326, p = 0.006), but negative correlations with serum levels of IGF-I (r = -0.340, p = 0.004). The radiological score, but not joint pain, also correlated with YKL-40 levels (r = 0.364, p = 0.002). As the functional disability of patients became severe, the serum YKL levels increased.
Serum YKL-40 levels partially reflect the degree of inflammation and also reflect the joint destruction in patients with RA.