Endocrine Abstracts

Objective: Despite the high sensitivity of TRAb measured by modern assay methods, some patients with Graves’ disease (GD) may still have normal TRAb levels. Therefore, the purpose of this study was to determine the clinical utility of TRAb measured by a third generation assay method, and to determine it’s relationship with clinical and laboratory parameters in Turkish patients with GD.

Methods: In this study, 328 consecutive treatment-naive patients with GD (248 female (%75.6), mean age 42±12.75 years old), who were admitted between January 2014-December 2018, were retrospectively analyzed. TRAB levels were assessed by electrochemiluminescence immunoassay (Elecsys 2010, Roche Cobase, Mannheim, Germany, manufacturer’s cut-off: 1.75 IU/L). TSH, fT3, and fT4 levels were assessed using a chemiluminescence immunoassay method. The goiter size of the participants were obtained from computer records. The diagnosis of GD with normal TRAb values was made according to clinical features and/or Tc-99m thyroid uptake values.

Results: Mean TRAb, TSH, fT3 and fT4 levels were 10.43±10,58 IU/l, 0.027±0.35 mIU/l, 10.88±6.36 pg/ml and 4.07±12.03 ng/dl, respectively. Fifty-eight (17.8%) patients with GD had normal TRAb levels. Mean TRAb levels were higher in male patients compared to female patients (13.98±11.61 vs 9.28±9.97 IU/l, P=0.001). GD with normal TRAb levels was more frequent in female patients compared to male patients (48 (19.5%) vs 10 (12.5%), P<0.001). A positive correlation was found between TRAb and fT3 levels (r=0.29, P<0.001). A strong positive correlation was also found between goiter size and TRAb levels (grade-1: 6.40±8.18 IU/l, grade-2: 12.04±10.84 IU/l and grade-3: 16.78±10.59 IU/l, P<0.001 for all comparisons). Nevertheless, no correlation was found between TRAb titers with fT4 levels and age (r=−0.015, P=0.44 and r=−0.02, P=0.67).

Conclusions: Despite of the reported high sensitivity and specificity of TRAb, measured by third generation assay methods, TRAb levels, measured by a third generation fully automated ECLIA, were normal in 17% of the cases with GD in this study. TRAb negative GD was more frequent among females and TRAb titers were also lower in females compared to male patients. Therefore, the presence of TRAb negative disease should always be taken into consideration in patients with hyperthyroidism, irrespective of the TRAb assay method used, and further studies should be performed to assess the clinical utility of TRAb, mesured by ECLIA in different populations with GD.