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Health Information For Parents
A T4 test measures the blood level of the hormone T4, also known as thyroxine, which is produced by the thyroid gland and helps control metabolism and growth. The T4 test is performed as part of an evaluation of thyroid function.
Two blood tests may be performed as part of a T4 test:
Doctors may order the T4 test if symptoms suggest any kind of thyroid disorder. For example, an overactive thyroid, called hyperthyroidism, is typically associated with symptoms like weight loss, a fast heart rate, and sweating.
An underactive thyroid, called hypothyroidism, may cause symptoms such as weight gain, fatigue, and feeling cold. Newborns are routinely screened for hypothyroidism, which can cause serious medical problems if left untreated.
No special preparations are needed for this test. However, certain medications, including seizure medication, cardiac drugs, steroids, birth control pills, and even aspirin can affect the results, so it’s important to tell the doctor about any medication your child is taking.
On the day of the test, having your child wear a T-shirt or short-sleeved shirt can make things easier for the technician drawing the blood.
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 A needle is inserted into a vein (usually in the arm inside of the elbow or on the back of the hand) and blood is withdrawn and collected in a vial or syringe.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 blood for this test will only take a few minutes.
Either method (heel or vein withdrawal) of collecting a sample of blood 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.
The blood sample will be processed by a machine. The results are usually available after a few hours or the next day.
In general, high T4 results may indicate hyperthyroidism and low T4 results may indicate hypothyroidism. However, in order for doctors to diagnose the specific type of thyroid problem, a more complete picture is obtained by performing the T4 test with other thyroid tests, such as those that measure thyroid-stimulating hormone (TSH), T3 (triiodothyronine), and thyroid antibodies.
The T4 test is considered a safe procedure. However, as with many medical tests, some problems can occur with having blood drawn. These include:
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 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 about the T4 test, contact your doctor.
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.
Doctors may order TSH blood tests to diagnose and monitor treatment of a thyroid disorder or evaluate pituitary gland functioning.
Doctors may order the T3 resin uptake when a child’s symptoms or previous blood tests seem to suggest thyroid dysfunction.
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.
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.
The thyroglobulin antibodies test is used to help diagnose autoimmune conditions involving the thyroid gland, or when thyroid disorders are suspected.
The glands of the endocrine system and the hormones they release affect almost every cell, organ, and function of our bodies.
These videos show what’s involved in getting a blood test and what it’s like to be the person taking the blood sample.
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.
A blood test might sound scary, but it usually takes less than a minute. Watch what happens in this video for kids.
Do you know just how important the thyroid is? It helps you grow and affects your energy level.
Note: All information is for educational purposes only. For specific medical advice, diagnoses, and treatment, consult your doctor.
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