What It Is

A thyroid stimulating hormone (TSH) test is a common blood test used to evaluate how well the thyroid gland is working. The thyroid gland is located at the lower front of the neck. TSH is produced by the pituitary, a pea-sized gland located at the base of the brain.

When the thyroid gland isn't producing enough thyroid hormone (called hypothyroidism), the pituitary gland produces more TSH in an attempt to stimulate the thyroid and increase its production of thyroid hormones. If the pituitary gland isn't functioning properly, it may produce too little TSH, and this can result in hypothyroidism as well.

If the thyroid gland is producing too much thyroid hormone (called hyperthyroidism), the pituitary gland produces less TSH in an attempt to decrease the thyroid's production of thyroid hormones.

Symptoms of hypothyroidism in children include tiredness, dry skin, constipation, slow growth, and delayed pubertal development. Hyperthyroidism can cause unexpected weight loss, a rapid or irregular heartbeat, sweating, nervousness, and irritability.

In both hypothyroidism and hyperthyroidism, the child may develop a goiter — a lump in the neck due to enlargement of the thyroid gland. Both conditions are treatable.

Why It's Done

TSH testing is used to:

• diagnose and monitor the treatment of a thyroid disorder
• help evaluate pituitary gland function

Your doctor may order a TSH test if your child has symptoms of hyperthyroidism or hypothyroidism, or shows signs of an enlarged thyroid gland. The TSH test also may be ordered at regular intervals to monitor the effectiveness of treatment if your child is being treated for a thyroid disorder.

TSH tests are routinely ordered for newborns in many states as part of the screening program to enable the prompt diagnosis and treatment of infants with congenital (present at birth) hypothyroidism.

Preparation

Your child doesn't have to fast or limit activity before the test. However, some medications may affect test results. Check with your doctor to see if you should discontinue any medications until after the test. Extreme stress and acute or chronic illness also can affect TSH test results.

Procedure

A health professional will usually draw the blood from a vein. For an infant, the blood may be obtained by puncturing the heel with a small needle (lancet). If the blood is being drawn from a vein, the skin surface is cleaned with antiseptic and an elastic band (tourniquet) is placed 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 blood sample is only temporarily uncomfortable and feels 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 within a day or two.

Whether your child's results are high or low, an abnormal TSH usually indicates an excess or deficiency in the amount of thyroid hormone available to his or her body. It does not, however, indicate what the specific problem is. To determine the cause, your doctor will usually do additional testing, such as measurement of the blood levels of the hormones produced by the thyroid gland itself.

Risks

The TSH test is considered a safe procedure. However, as with many medical tests, some problems can occur with having blood drawn:

• 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 TSH test procedure, speak with your doctor. You can also talk to the technician before the procedure.

Reviewed by: Steven Dowshen, MD
Date reviewed: April 2011