The overall prevalence of the development of autoantibodies that target thyroid tissue receptors or interfere with the regulation of thyroid function has been reported to be as high as 1 in 4 adult women.
The identification of specific thyroid antibodies through laboratory analysis permits the elucidation of the autoimmune mechanism. The most common thyroid autoantibodies include:
- Thyrotropin receptor antibody (TRAb)
- Also known as thyroid-stimulating immunoglobulins (TSI)
- Thyroperoxidase antibody (TPOAb)
- Thyroglobulin antibody (TgAb)
- Thyroxine-binding globulin antibody (TBGAb)
TSIs are IgG antibodies that can bind to thyrotropin (TSH) receptors on the thyroid gland. TSIs mimic the action of TSH, causing excess secretion of thyroxine and triiodothyronine. The TSI level is abnormally high in persons with hyperthyroidism due to Graves' disease, discussed in greater detail on the next page.
TPO is a membrane-associated protein expressed only in thyroid follicular cells. This enzyme is responsible for the oxidation of iodide on the tyrosine residues in thyroglobulin for the synthesis of T3 and T4. Autoantibodies directed against TPO limit its activity and impart a negative effect on the production of the thyroid hormone. TPOAb levels are the highest in Hashimoto's thyroiditis, discussed in greater detail on an upcoming page.
TgAbs are directed specifically against the globulin protein that is produced and stored in the thyroid follicles. Its presence alone is not diagnostic of a specific thyroid autoimmune disorder and is often found in conjunction with other anti-thyroid antibodies. Determining TgAb is essential when monitoring thyroglobulin as a tumor marker for the recurrence of thyroid carcinoma.
TBGAbs are directed against thyroxine-binding globulin (TBG), which is primarily responsible for thyroid hormone transport. TBG has a greater affinity for binding to T4.
