What Is the Thyroid? The thyroid is a small gland below the skin and muscles at the front of the neck, at the spot where a bow tie would rest. It makes two types of thyroid hormones: T3 (triiodothyronine) and T4 (thyroxine). It helps the body do many things, such as get energy from food, grow, and go through sexual development. The pituitary is a pea-sized gland at the bottom of the brain that makes thyroid stimulating hormone (TSH). TSH triggers the thyroid to make more thyroid hormone. The pituitary gland and the thyroid gland send messages back and forth to each other about how much hormone to make to keep the levels normal. What Is Thyroid Disease? Some diseases of the thyroid or pituitary gland cause the thyroid to make too much or not enough thyroid hormone: If the thyroid is overactive, it releases too much thyroid hormone, causing hyperthyroidism. The body use up energy more quickly than it should, and chemical activity (like metabolism) in the cells speeds up. Symptoms include sweating, trembling, weight loss, and fast heartbeat. If the thyroid is underactive, it makes too little thyroid hormone, causing hypothyroidism. The body uses up energy more slowly, and chemical activity (metabolism) in the cells slows down. Symptoms include tiredness, feeling cold, constipation, dry skin, and slow height growth in children. What Are Thyroid Blood Tests? Doctors use blood tests to check for thyroid or pituitary problems. In kids already diagnosed with thyroid or pituitary problems, the tests are used to guide treatment. Commonly ordered thyroid blood tests include: T4 test: This is done to measure the blood level of the hormone T4 (thyroxine). It might be done in one or both of the following ways: total T4, which measures the entire amount of thyroxine in the blood, including the amount attached to blood proteins that help carry the hormone through the bloodstream free T4, which measures only the thyroxine that's not attached to proteins. This is the part of T4 in the blood that affects how the body's cells work.The results of the T4 blood tests can help diagnose hyperthyroidism or hypothyroidism and guide treatment. TSH test: A thyroid stimulating hormone (TSH) test can help tell how well the thyroid is working. If a thyroid disease prevents the gland from making enough thyroid hormone, the pituitary gland releases more TSH into the blood. If the thyroid is making too much thyroid hormone, the pituitary releases less TSH, which can lower the levels of TSH in the blood. T3 total test: The T3 total test measures the other major thyroid hormone in the blood. It often helps doctors diagnose hyperthyroidism. thyroid antibodies test: Hashimoto's thyroiditis is an autoimmune condition in which the immune system attacks the thyroid gland. To diagnose it, doctors check for high levels of antibodies that are a sign of the immune system's attack on proteins in the thyroid gland. Usually, two types of thyroid antibodies are measured: thyroglobulin antibodies (TgAb) and thyroid peroxidase antibodies (TPO). In some cases, abnormal thyroid test results can be due to a medicine, an ongoing medical condition, or pregnancy. In these cases, there may be nothing wrong with the thyroid or pituitary glands themselves. The normal ranges of thyroid function test results vary by age. Doctors think about this carefully when they interpret them. What if I Have Questions? If you have any questions about a thyroid blood test, speak with your doctor. You can also talk to the technician who's doing the blood draw before the procedure. Back to Articles Related Articles Thyroid Disease The thyroid gland makes the hormones that help control metabolism and growth. A thyroid that isn't working properly can cause thyroid disease. Read More Hyperthyroidism and Graves’ Disease Hyperthyroidism happens when the thyroid gland sends too much thyroid hormone into the blood. The most common cause of hyperthyroidism is Graves' disease. Read More Hypothyroidism and Hashimoto’s Thyroiditis An underactive thyroid makes too little thyroid hormone, causing hypothyroidism. Hashimoto's thyroiditis, which causes most cases of hypothyroidism in kids and teens, is a condition in which the immune system attacks the thyroid. Read More Congenital Hypothyroidism Some babies are born with a thyroid gland that didn't develop correctly or doesn't work as it should. This is called congenital hypothyroidism. Read More Goiters and Thyroid Nodules An enlarged thyroid gland is a lump that can be felt under the skin at the front of the neck. When it's big enough to see easily, it's called a goiter. A thyroid nodule is a lump or enlarged area in the thyroid gland. Read More Blood Test: Thyroid Peroxidase Antibodies 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. Read More Blood Test: Thyroid Stimulating Hormone (TSH) Doctors may order TSH blood tests to diagnose and monitor treatment of a thyroid disorder or evaluate pituitary gland functioning. Read More Blood Test: T3 Resin Uptake (T3RU) Doctors may order the T3 resin uptake when a child's symptoms or previous blood tests seem to suggest thyroid dysfunction. Read More Blood Test: T3 Total (Triiodothyronine) 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. Read More Blood Test: T4 (Thyroxine) Doctors may order the T4 blood test if symptoms suggest any kind of thyroid disorder. Read More Blood Test: Thyroglobulin Antibodies (TgAb) The thyroglobulin antibodies test is used to help diagnose autoimmune conditions involving the thyroid gland, or when thyroid disorders are suspected. Read More CAT Scan: Neck A neck CAT scan can detect signs of disease in the throat and surrounding areas. Doctors may order one to detect abscesses, birth defects, cysts, or tumors. Read More Thyroid Cancer Thyroid cancer is uncommon in kids. Most who develop it do very well when the cancer is found and treated early. Read More What Is the Thyroid? Do you know just how important the thyroid is? It helps you grow and affects your energy level. Read More Note: All information is for educational purposes only. For specific medical advice, diagnoses, and treatment, consult your doctor. © 1995-2021 KidsHealth®. All rights reserved. Images provided by The Nemours Foundation, iStock, Getty Images, Veer, Shutterstock, and Clipart.com.