What It Is A thyroglobulin antibodies (TgAb) test is used to check blood levels of antibodies the body has made against the compound thyroglobulin. Thyroglobulin is a protein produced and used by the thyroid gland (the small, butterfly-shaped gland in the neck) to make the hormones triiodothyronine (T3) and thyroxine (T4), both of which help control metabolism and growth. Ordinarily, a healthy immune system wouldn't make significant levels of antibodies against thyroglobulin, because it's not "foreign," but rather a necessary component of thyroid functioning. Antibodies are proteins made by the immune system to fight bacteria, viruses, and toxins. In autoimmune diseases, however, the immune system malfunctions, mistakenly attacking healthy organs and tissues as though they were foreign invaders. In people with certain thyroid-related autoimmune conditions, the blood level of thyroglobulin antibodies may rise. Why It's Done The thyroglobulin antibodies test is used primarily to help diagnose autoimmune conditions involving the thyroid gland. The test may be ordered when a child has symptoms of a thyroid disorder, including thyroiditis (inflammation of the thyroid) or goiter (an enlarged thyroid), or if tests to check blood levels of T3, T4, or thyroid stimulating hormone (TSH) showed abnormalities. Preparation No special preparations are needed for this test. On the day of the test, having your child wear a T-shirt or short-sleeved shirt can make things easier for your child and the technician who will be drawing the blood. The Procedure A health professional will draw the blood from a vein, after cleaning the skin surface with antiseptic, and placing an elastic band (tourniquet) around the upper arm to apply pressure and cause the veins to swell with blood. A needle is inserted into a vein (usually in the arm inside of the elbow or on the back of the hand) and blood is withdrawn and collected in a vial or syringe. After the procedure, the elastic band is removed. Once the blood has been collected, the needle is removed and the area is covered with cotton or a bandage to stop the bleeding. Collecting the blood for the test will only take a few minutes. What to Expect Collecting a sample of blood for this test is only temporarily uncomfortable and can feel like a quick pinprick. Afterward, there may be some mild bruising, which should go away in a few days. Getting the Results The blood sample will be processed by a machine, and results are commonly available after a few days. Risks The thyroglobulin antibodies test is considered a safe procedure. However, as with many medical tests, some problems can occur with having blood drawn, such as: fainting or feeling lightheaded hematoma (blood accumulating under the skin causing a lump or bruise) pain associated with multiple punctures to locate a vein Helping Your Child Having a blood test is relatively painless. Still, many children are afraid of needles. Explaining the test in terms your child can understand might help ease some of the fear. Allow your child to ask the technician any questions he or she might have. Tell your child to try to relax and stay still during the procedure, as tensing muscles and moving can make it harder and more painful to draw blood. It also may help if your child looks away when the needle is being inserted into the skin. If You Have Questions If you have questions about the thyroglobulin antibodies test, speak with your doctor. Back to Articles Related Articles A to Z: Hashimoto's Thyroiditis Hashimoto's thyroiditis is a chronic (ongoing) condition where the body's immune system attacks the thyroid, a gland in the neck that makes thyroid hormone. Read More Getting a Blood Test (Video) A blood test might sound scary, but it usually takes less than a minute. Watch what happens in this video for kids. Read More Blood Test (Video) These videos show what's involved in getting a blood test and what it's like to be the person taking the blood sample. Read More Blood Test: Thyroid Stimulating Hormone (TSH) Doctors may order TSH blood tests to diagnose and monitor treatment of a thyroid disorder or evaluate pituitary gland functioning. Read More Blood Test: T3 Total (Triiodothyronine) The T3 total test is part of an evaluation of thyroid function. It's particularly useful in diagnosing hyperthyroidism, which can cause symptoms such as a fast heart rate, weight loss, trembling and sweating. Read More Blood Test: Thyroid Peroxidase Antibodies The thyroid peroxidase antibodies test is primarily used to help diagnose and monitor autoimmune conditions involving the thyroid gland, including Hashimoto's thyroiditis and Graves disease. Read More What Is the Thyroid? Do you know just how important the thyroid is? It helps you grow and affects your energy level. Read More Endocrine System The glands of the endocrine system and the hormones they release affect almost every cell, organ, and function of our bodies. Read More What Are Glands? You've heard of glands, but what are they? Find out in this article for kids. Read More Endocrine System The endocrine system influences almost every cell, organ, and function of our bodies. It is instrumental in regulating mood, growth and development, metabolism, and sexual function, among other things. Read More Blood Test: T4 (Thyroxine) Doctors may order the T4 blood test if symptoms suggest any kind of thyroid disorder. Read More Note: All information is for educational purposes only. For specific medical advice, diagnoses, and treatment, consult your doctor. © 1995-2021 KidsHealth®. All rights reserved. Images provided by The Nemours Foundation, iStock, Getty Images, Veer, Shutterstock, and Clipart.com.