Thyroglobulin Antibodies (TgAb)

Your thyroid is a small, butterfly-shaped gland located near your throat. It makes hormones that control how your body uses energy. Thyroid hormones affect everything from your heart rate to how fast you burn calories from food. If antibodies attack your thyroid cells, your thyroid may not work properly.

Thyroid antibodies can cause autoimmune diseases such as Hashimoto's disease, which leads to hypothyroidism (an underactive thyroid that makes too little thyroid hormone), or Graves' disease, which causes hyperthyroidism (an overactive thyroid that makes too much thyroid hormone).

You may need this test if you have symptoms of a thyroid disorder. Symptoms of Hashimoto's disease (hypothyroidism) include weight gain, fatigue, hair loss, sensitivity to cold, irregular menstrual periods, constipation, depression, and joint or muscle pain. Symptoms of Graves' disease (hyperthyroidism) include weight loss, bulging of the eyes, hand tremors, sensitivity to heat, trouble sleeping, anxiety, increased heart rate, and goiter (an enlargement of the thyroid).

If you are having thyroglobulin (Tg) levels checked along with thyroid antibodies, the antibody result also matters because thyroglobulin antibodies can interfere with thyroglobulin testing and cause the Tg result to look lower than it really is.

If your results were negative, it means little or no thyroglobulin antibodies were found in your blood. Your symptoms may be caused by something other than autoimmune thyroid disease.

Positive TgAb supports a diagnosis of autoimmune thyroid disease, most often Hashimoto's thyroiditis (an autoimmune cause of an underactive thyroid). About 30 to 50% of people with autoimmune hypothyroidism are TgAb-positive, and TgAb is also seen in some people with Graves' disease.

In thyroid cancer follow-up, the main reason TgAb is checked is that it can throw off the thyroglobulin (Tg) test result. About 1 in 5 thyroid cancer patients are TgAb-positive, and in those people the Tg result may look falsely low; your provider may use a special method (mass spectrometry) to measure Tg accurately.

In general, the higher the levels of antibodies, the more likely it is that you have an autoimmune thyroid disorder. But your provider will look at your antibody test results along with your symptoms and the results of other thyroid tests to make a diagnosis.

If you are diagnosed with an autoimmune thyroid disorder, there are medicines that can help manage your condition. If you have questions about your results, talk with your provider.