A thyroid peroxidase antibodies test checks the levels of antibodies made against
the compound thyroid peroxidase (TPO) in the bloodstream. Thyroid peroxidase is an
enzyme produced by the thyroid gland. The thyroid is a small, butterfly-shaped gland
in the neck that uses iodine, with the help of the enzyme TPO, to create the
hormones triiodothyronine (T3) and thyroxine (T4), both of which help control metabolism
and growth. Antibodies are proteins made by the immune system, usually to fight bacteria,
viruses, and toxins that enter or contact the body.
Ordinarily, a healthy immune system doesn't make significant levels of antibodies
against thyroid peroxidase, because it's not "foreign," but rather a necessary component
of thyroid tissue.
In autoimmune diseases, however, the immune system malfunctions, mistakenly attacking
healthy organs and tissues as though they were foreign invaders. In people with a
thyroid-related autoimmune condition, the blood level of TPO antibodies may rise.
Why It's Done
The thyroid peroxidase antibodies test is primarily used to help diagnose and monitor
autoimmune conditions involving the thyroid gland, such as Hashimoto's thyroiditis
and Graves disease.
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 thyroid gland function, such as levels of thyroid hormones or thyroid stimulating
hormone (TSH), show 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(usually in the arm inside of the elbow or on the back of the hand) and blood is withdrawn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. Collecting
blood for this test will only take a few minutes.
What to Expect
Collecting a blood sample is only temporarily uncomfortable and can feel like a
quick pinprick. Afterward, there may be some mild bruising, which should go away in
a day or so.
Getting the Results
The blood sample will be processed by a machine. The results are commonly available
after a few days.
The thyroid peroxidase antibodies test is considered a safe procedure. However,
as with many medical tests, some problems can occur with having blood drawn, such
fainting or feeling lightheaded
hematoma (blood accumulating under the skin causing a lump or a bruise)
pain associated with multiple punctures to locate a vein
Helping Your Child
Having a blood test is relatively painless. Still, many kids are afraid of needles.
Explaining the test in terms your child can understand might help ease some of the
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 for
your child to look away when the needle is being inserted into the skin.
If You Have Questions
If you have questions about the thyroid peroxidase antibodies test, speak with
your doctor. You can also talk to the technician before the procedure.