The characteristics and clinical significance of serum TRAb IgG subtype in patients with thyroid associated ophthalmopathy

Abstract

Objective To explore the distribution of serum TRAb IgG subtypes in patients with thyroid-associated ophthalmopathy(TAO) at different stages and its value in assessing TAO activity. Methods Forty-three patients with TAO, 30 patients with Graves′ disease (GD group), 19 patients with Hashimoto′s thyroiditis (HT group), and 50 healthy subjects (NC group)admitted to the First Affiliated Hospital of Zhengzhou University were collected from August 2018 to February 2019. According to the clinical activity score (CAS), the patients with TAO were further divided into the active period group (AP group, CAS≥3 points, 22 cases) and the inactive period group (IP group, CAS<3 points, 21 cases). The basic clinical data of subjects in each group were collected. The serum concentrations of FT3, FT4, TSH, thyroperoxidase antibody (TPOAb), thyroglobulin antibody (TgAb), and thyroid-stimulating hormone receptor antibody (TRAb) were detected by chemiluminescence immunoassay and the binding rate in percentage (B) of serum TRAb IgG and IgG subtypes were detected by ELISA. The positive rate in each group and relative content of positive samples were compared. Results (1)Compared with HT group, the positive rates of IgG1 and IgG2 in TAO group and GD group were significantly decreased (P 0.05). (2)Compared with the IP group, IgG1(B) and the positive rates of IgG1 in the AP group were increased while IgG4(B) and the relative contents of IgG4 were reduced (P<0.05). (3)IgG1(B)was positively correlated with TAO activity (B=6.190, P=0.007), and higher IgG4(B)indicated more inclinations to the inactive period (B=-16.390, P=0.052). (4) The area under the curve of receiver operating characteristic (ROC) for TAO developing into active period assessed by activity rate was 0.859 (95%CI 0.746-0.973, P<0.05). When the activity rate was 4.29, the Jordon index showed the largest, with sensitivity of 81.8% and specificity of 81.0%. Conclusions Elevated levels of TRAb IgG1 in the patients with TAO indicate a tendency to active period, while elevated levels of TRAb IgG4 indicate a tendency to inactive period. The activity rate can provide a reference for assessing whether TAO is active or not. Key words: Thyroid-associated ophthalmopathy; IgG subtype; Clinical activity score