What are Thyroid Antibodies?

Understanding Autoimmune Test Results for Thyroid Problems

Sep 14, 2009 Melissa Murfin

Thyroid antibody tests are often ordered to determine if a patient has an autoimmune thyroid condition. Find out more about what these thyroid levels mean.

In most cases, thyroid disorders are autoimmune where the immune system creates antibodies against a normal part of the body. Thyroid antibodies attack the thyroid, causing changes in thyroid function. The thyroid may be damaged by some antibodies so that it no longer produces enough thyroid hormone. This leads to hypothyroidism and is known as Hashimoto's thyroiditis. Other thyroid antibodies stimulate the thyroid to produce too much thyroid hormone, resulting in an overactive thyroid. This is called Graves' disease.

Blood tests are ordered in someone with abnormal TSH, T4 or T3 to give more information on the cause of the thyroid disorder. These antibody tests are called TPO antibody, Tg antibody, TSI, TBII and TrAb.

Thyroid Peroxidase Antibody (TPO)

The TPO test measures an antibody that is found in most patients with Hashimoto's hypothyroidism. This antibody blocks an enzyme that is responsible for adding iodine to a protein in thyroid hormone production. It is elevated in 85% to 90% of patients with hypothyroidism. The normal thyroid antibody level ranges from 0 to 34 IU/ml. Sometimes the levels can seem alarmingly high, even in the thousands. Thyroid antibody tests are read as positive or negative. The number itself is not cause for concern. Most patients with Hashimoto's hypothyroidism will always have positive thyroid antibodies.

Antithyroglobulin Antibody (Tg Ab)

This antibody blocks a protein made by the thyroid that is necessary for making thyroid hormones, T4 and T3. It is positive in patients with Hashimoto's thyroiditis. This antibody level may also be elevated in other autoimmune conditions such as rheumatoid arthritis, lupus and Sjogren's syndrome. Antithyroglobulin antibody is also used to monitor patients who have had thyroid cancer for recurrence. This test should be negative in most patients who have had their thyroid removed.

Thyroid Receptor Antibodies (TRAb)

Thyroid receptor antibodies are tested in patients with Graves' hyperthyroidism. Thyroid-stimulating immunoglobulin (TSI) and thyrotropin-binding inhibitory immunoglobulin (TBII) are also implicated in Graves disease. These antibodies attack the thyroid, stimulating it to produce excess thyroid hormone. Levels often improve to normal with treatment. When these antibody levels remain elevated, the prognosis for cure of Graves' disease is not as good. Stimulating antibodies are the cause of thyroid eye disease because they also attack eye tissues in addition to the thyroid.

Thyroid antibody tests offer more information on the autoimmune nature of thyroid disease. Patients should check with their health care provider for more information on testing.

Sources:

LabCorp

American Thyroid Association

The copyright of the article What are Thyroid Antibodies? in General Medicine is owned by Melissa Murfin. Permission to republish What are Thyroid Antibodies? in print or online must be granted by the author in writing.

George Bush had Graves' Disease

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