Low titers of thyroid autoantibodies may be observed in the absence of autoimmune or other thyroid diseases and are considered a nonspecific finding. The population prevalence of such nonspecific low-level anti-Tg positivity is higher in females than in males and increases with age in both genders.
Detection of significant titers of anti-Tg or anti-TPO autoantibodies is supportive evidence for a diagnosis of Graves disease in patients with thyrotoxicosis. However, measurement of the pathogenic anti-TSH receptor antibodies by binding assay or bioassay is the preferred method confirming Graves disease in atypical cases and under special circumstances.
Patients with nodular thyroid disease who are anti-thyroid autoantibody positive may have coexisting Hashimoto disease, which can result in a suspicious fine-needle aspiration biopsy diagnosis of follicular or Hurthle cell neoplasia.
Anti-Tg values determined by different methodologies might vary significantly and cannot be directly compared with one another. Some patients might show to be antibody-positive by some methods and antibody-negative by others. Comparing anti-Tg antibody values from different methods might lead to erroneous clinical interpretation.
In patient receiving therapy with high biotin doses (ie, >5 mg/day), no specimen should be drawn until at least 8 hours after the last biotin administration.
Tg concentrations >2,000 ng/mL may lead to falsely elevated anti-Tg concentrations.