Thyroid antibody tests detect the presence of specific antibodies against thyroid tissue and are used to diagnose and monitor autoimmune thyroid diseases. Here are the primary thyroid antibody tests:
- Thyroid Peroxidase Antibodies (TPOAb):
- Target: Thyroid peroxidase enzyme, which plays a role in the production of thyroid hormones.
- Clinical Relevance: These antibodies are most commonly elevated in Hashimoto’s thyroiditis (chronic autoimmune thyroiditis) and in Graves’ disease. They can be found in other thyroid diseases and even in individuals without apparent thyroid dysfunction.
- Thyroglobulin Antibodies (TgAb):
- Target: Thyroglobulin, a key protein in the thyroid gland involved in the production of thyroid hormones.
- Clinical Relevance: Like TPOAb, these antibodies are typically elevated in Hashimoto’s thyroiditis and may also be raised in Graves’ disease. They can be a hindrance in the use of serum thyroglobulin as a tumor marker in differentiated thyroid cancer, as the presence of the antibodies can interfere with the measurement of thyroglobulin levels.
- Thyroid Stimulating Hormone Receptor Antibodies (TSH-RAb):
- There are different types of TRAb, and they can either stimulate the TSH receptor (as in Graves’ disease) or block it.
- Thyroid-stimulating immunoglobulins (TSI): These are a subtype of TRAb that stimulate the TSH receptor, leading to increased thyroid hormone production, as seen in Graves’ disease.
- TSH binding inhibitory immunoglobulins (TBII): These block the receptor.
- Clinical Relevance: These antibodies are primarily associated with Graves’ disease. A high level of TSI is characteristic of Graves’ disease and is responsible for the hyperthyroidism seen in these patients.
- There are different types of TRAb, and they can either stimulate the TSH receptor (as in Graves’ disease) or block it.
When suspecting an autoimmune thyroid disease, typically TPOAb and TgAb are ordered first. If Graves’ disease is suspected, TSH-RAb or its subtypes might be ordered to confirm the diagnosis.