The thyroid makes hormones that do many important things, such as helping with brain development, growth, pubertal development, and how the body uses energy. Thyroid function tests help health care providers see how well the thyroid is working. Kids can have abnormal test results for different reasons. Here's what to do next.

Follow your health care provider's instructions for:

• going to see an endocrinologist (a doctor who diagnoses and treats problems with hormones)
• whether your child needs to take any medicines

You have any questions.

What causes abnormal thyroid function test results? Abnormal thyroid test results can mean someone has hypothyroidism (low levels of thyroid hormone) or hyperthyroidism (high levels of thyroid hormone). Many things can cause hyper/hypothyroidism, such as genetic (inherited) or autoimmune (where the body attacks its own cells) conditions or being born with a thyroid that doesn't work normally. These conditions usually need treatment with thyroid medicines.

Abnormal results can also be due to certain medicines, vitamin supplements (biotin), or an infection. Thyroid medicine is not usually needed because the test results usually go back to normal when the medicine or vitamin is stopped, or the infection gets better.

What is measured in thyroid function tests? Thyroid function tests include:

• Thyroid stimulating hormone (TSH): TSH is made by the pituitary gland in the brain. In hypothyroidism, the TSH level goes up to stimulate the thyroid to make more hormones. In hyperthyroidism, TSH levels go down so the thyroid makes less hormones.
• Free T3 and T4: This is the active part of the hormone.
• Total T3 and T4: This includes the free T3 and T4 and the T3 and T4 that is stored for later use.
• Thyroid antibodies: High levels of antibodies are a sign that the immune system is attacking the thyroid gland. Usually, two types of thyroid antibodies are measured: thyroglobulin antibodies (TgAb) and thyroid peroxidase antibodies (TPO).

Health care providers order different thyroid function tests for different reasons. For example, a TSH level can check how someone's thyroid is working overall, and a free T4 can see how medicine is working in certain types of thyroid illnesses.