Blood Test: Thyroglobulin Antibodies (TgAb) (for Parents) – Nemours KidsHealth

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.

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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 A needle is inserted into a vein (usually in the arm inside of the elbow or on the back of the hand) and blood is withdrawn and collected in a vial or syringe.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.