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Thyroid Tests

What Is the Thyroid?

The thyroid is a small gland located below the skin and muscles at the front of the neck, just 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). The pituitary gland and the thyroid gland send messages back and forth to each other about how much hormone to make.

What Is Thyroid Disease?

Thyroid disease is when the thyroid gland doesn't supply the proper amount of hormones needed by the body.

  • If the thyroid is overactive, it releases too much thyroid hormone into the bloodstream, causing hyperthyroidism.The body use up energy more quickly than it should, and chemical activity (like metabolism) in the cells speeds up.
  • 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.

What Are Thyroid Blood Tests?

Doctors use blood tests to check for thyroid or pituitary problems. In kids who are already diagnosed with thyroid or pituitary problems, the tests can show how well treatment is working.

Thyroid function blood tests usually are done together (called a thyroid panel). They include:

  • TSH test: A thyroid stimulating hormone (TSH) test is used to evaluate how well the thyroid gland is working and to check the effectiveness of thyroid disorder treatments. The test also is a routine part of newborn screening to check for congenital hypothyroidism.
  • T3 resin uptake testDone along with other thyroid tests, the T3RU measures the level of a protein called thyroxin-binding globulin (TBG) that carries the thyroid hormones triiodothyronine (T3) and thyroxine (T4). It's done to help diagnose hyperthyroidism and hypothyroidism.
  • T3 total testThe T3 total test, the most common type of T3 blood test, measures both the bound form (attached to and carried by proteins) and free forms (not attached to proteins) of triiodothyronine. It's particularly useful in diagnosing hyperthyroidism.
  • T4 test: This is done to measure the blood level of the hormone T4 (thyroxine). It might be done in two parts: one measures total T4, and the other measures free T4 (thyroxine that's not attached to proteins). The results can help diagnose hyperthyroidism or hypothyroidism.
  • thyroglobulin antibodies test: A TgAb test checks blood levels of antibodies the body has made against thyroglobulin (a protein made and used by the thyroid). In thyroid-related autoimmune conditions, the immune system mistakenly attacks the thyroid, causing the blood level of thyroglobulin antibodies to rise. High levels can indicate thyroiditis (inflammation of the thyroid) or a goiter (enlarged thyroid).
  • thyroid peroxidase antibodies test: A TPO test checks blood levels of antibodies made against thyroid peroxidase (an enzyme made by the thyroid). A thyroid-related autoimmune condition, such as Hashimoto's thyroiditis, can make the blood level of TPO antibodies rise.

In some cases, abnormal thyroid test results can be due to certain medicines, an ongoing medical condition, or pregnancy. In these situations, there may be nothing wrong with the thyroid or pituitary glands themselves.

The normal ranges of thyroid function test results vary by age, and kids can have abnormal results for different reasons. Doctors think about this carefully when they interpret them.

What Are Thyroid Nodule Tests?

Doctors usually discover thyroid nodules by touch during a physical examination. If the doctor finds a nodule, thyroid function blood tests can help them see how the thyroid is working. A doctor also may order an ultrasound of the thyroid to see if the nodule is a cyst or a solid growth or tumor.

Another test, called a thyroid scan, can tell the doctor what type of nodule someone has. For this test, a person swallows a pill containing a small amount of radioactive iodine or another radioactive substance (a "tracer"). The thyroid absorbs the radioactive substance. Then, a special camera measures where the radioactive substance is taken up by the thyroid gland, giving the doctor a better picture of the location, size, and type of thyroid nodule. It also can show if the cancer has spread.

A fine-needle biopsy also might be done to see if a nodule is cancerous. During the biopsy, the doctor inserts a thin needle through the skin into the thyroid nodule (the skin is numbed with medicine first). Through the needle, the doctor takes a sample of tissue or some fluid from a cyst. The tissue or fluid is then sent to a lab to be examined. In some cases, a person might need to have the nodule surgically removed for more detailed examination in the lab.

Thyroid cancer is uncommon in kids and teens. Even when cancer is the cause, the results of treatment are usually excellent.