What are thyroid hormone tests?

Thyroid hormone tests are blood tests that check how well your thyroid gland is working. The thyroid gland is a butterfly-shaped gland that lies in front of your windpipe (trachea), just below your voice box (larynx). The thyroid gland makes hormones that control the way your body uses energy (metabolism).

This test will give your doctor information about your thyroid hormone levels. You may have hyperthyroidism when your thyroid gland makes too much thyroid hormone. You may have hypothyroidism when the gland does not make enough thyroid hormone.

Why is this test done?

Thyroid hormone tests are done to find the cause of an abnormal thyroid-stimulating hormone (TSH) test. TSH tests can also check how well treatment for thyroid disease is working. They are used in newborns to find out if the thyroid gland is working as it should.

How do you prepare for the test?

If you are taking thyroid medicines, tell your doctor when you took your last dose. You may need to stop taking thyroid medicines for a short time before having this test.

How is the test done?

Blood test

A health professional uses a needle to take a blood sample, usually from the arm.

Heel stick

A heel stick is used to get a blood sample from a baby. The baby's heel is poked, and several drops of blood are collected. The baby may have a tiny bruise where the heel was poked.

What happens after the test?

• You will probably be able to go home right away.
• You can go back to your usual activities right away.

When should you call for help?

Watch closely for changes in your health, and be sure to contact your doctor or nurse advice line if you have any questions about this test.