Autoimmune thyroid disease is characterized by the presence of circulating autoantibodies directed to thyroid antigens. Hashimoto and Graves diseases are the best known of these diseases. The majority can be diagnosed by clinical presentation and their antibody profiles to thyroglobulin and thyroid microsomes. Therefore, immunoassays for thyroid antibodies are useful for diagnostic evaluations of thyroid autoimmune disease.
o Thyroglobulin is a water soluble glycoprotein that is involved in the storage and synthesis of thyroid hormones.
o The thyroid microsomal antigen has been shown to be the enzyme thyroid peroxidase (TPO).
Antibodies to thyroglobulin and or microsomal antigen are present in most patients with goitrous thyroiditis (Hashimoto disease), atrophic thyroiditis (myxedema) and about 70-90% of Graves disease. Antibodies are also found in about half of the patients with primary hypothyroidism and thyrotoxicosis, and 10-20% of patients with simple goiters and thyroid tumors. There is also a relationship between thyroid antibodies and diabetes mellitus. Thyroid autoantibodies are present in about 6-7% of normals and their incidence increases with age.
Classically, autoantibodies to thyroid antigens are detected by precipitation reactions, hemag-glutination and by immunoflourescence. However the tests are subjective and lack high sensitivity. Enzyme-Linked Immunosorbent Assays (ELISAs) combine greater sensitivity, objective reading and ease of use. ELISAs have been developed and validated for detecting autoantibodies to thyroid antigens.