Increased YKL-40 levels are linked with disease severity of initially diagnosed Graves' disease.

YKL-40, which is also known as Chitiniase 3-like 1, has been found to be up-regulated in many autoimmune diseases including asthma, systemic sclerosis and systemic lupus, etc. However, the relationship between serum levels of YKL-40 and one another common autoinmmue thyroid disease - Graves' disease (GD) has not yet been investigated. The current study was performed to investigate the correlation of serum YKL-40 levels with disease severity of initially diagnosed GD. A total of 142 newly diagnosed active GD and 137 healthy individuals were enrolled in the study. Methimazole was given to 55 GD patients and then 2-month study of follow-up was performed. A commercial ELISA kit was applied for the detection of YKL-40 in serum. Degree of goiter was assessed according to Pérez's Grade. Receiver operating characteristic (ROC) curve analysis was carried out to detect the diagnostic value of serum YKL-40 with regard to goiter degree. The velocity of the peak systolic blood-flow and the thyroid tissue blood flow (TBF) were examined using Color Flow Doppler ultrasonography (CFDU). The patients with GD exhibited dramatically higher YKL-40 in serum compared to those of healthy controls (606.1 ± 149.8 pg/mL vs. 397.4 ± 95.1 pg/mL,  < 0.001). Positive associations of YKL-40 with free T3 (FT3) and T4 (FT4), as well as the negative correlation of YKL-40 with TSH in serum, were observed. Additionally, the YKL-40 in serum was dramatically reduced after methimazole intervention, and the correlation of the decline with the reduced FT3 and FT4 was also found (all  < 0.001). Serum YKL-40 levels were positively correlated with goiter degree. ROC curve analysis demonstrated that serum YKL-40 concentration may act as a decent marker for goiter degree. The positive correlations of YKL-40 in serum with the average superior thyroid artery velocity (STV) and thyroid tissue blood flow (TBF) were also observed. Our findings implicated that YKL-40 may be closely connected to the pathogenesis of GD. Increased YKL-40 levels are linked with disease severity of initially diagnosed GD.