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
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
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.
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.
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blood is withdrawn and collected in a vial or syringe.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.
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