Skip to main content

Thyroid Function Test

Medically reviewed by Last updated on Sep 3, 2023.

What is a thyroid function test?

A thyroid function test is a blood test that checks your thyroid hormone levels. Your thyroid gland makes triiodothyronine (T3) and thyroxine (T4) hormones. These hormones help control body temperature, heart rate, growth, and weight. Thyroid stimulating hormone (TSH) helps balance thyroid levels by telling the thyroid when to produce thyroid hormones. TSH is made in the pituitary gland. Thyroid function tests may be done to check your blood levels of T3, T4, or TSH. These and other tests may be done to check how well your thyroid works.

Thyroid and Parathyroid Glands

Why do I need a thyroid function test?

You may need this test if you have symptoms of hyperthyroidism or hypothyroidism. Hyperthyroidism is a condition that is caused by thyroid hormone levels that are too high. Hyperthyroidism can lead to weight loss, sweating, a fast heartbeat, trouble sleeping, and other symptoms. Hypothyroidism is a condition that develops when your thyroid hormone levels are too low. Hypothyroidism may cause weight gain, fatigue, sensitivity to cold, thinning hair, depression, and other symptoms. This test may instead be done to check how well your thyroid medicine is working.

How do I prepare for the test?

This blood test may be done any time during the day. Certain medicines can affect the results of your thyroid test. Ask your healthcare provider if you should wait to take your medicines until after your blood is taken. Wear a short-sleeved or loose shirt on the day of the test. This will make it easier to draw your blood.

What do I need to know about my test results?

Your healthcare provider will discuss your test results with you. You may need to return for more tests if your test results are abnormal. You will need to take medicine if you have hyperthyroidism or hypothyroidism. If you are already taking medicine for these conditions, your dose may need to be changed.

Care Agreement

You have the right to help plan your care. To help with this plan, you must learn about your lab tests. You can then discuss the results with your healthcare providers. Work with them to decide what care may be used to treat you. You always have the right to refuse treatment.The above information is an educational aid only. It is not intended as medical advice for individual conditions or treatments. Talk to your doctor, nurse or pharmacist before following any medical regimen to see if it is safe and effective for you.

© Copyright Merative 2023 Information is for End User's use only and may not be sold, redistributed or otherwise used for commercial purposes.

Further information

Always consult your healthcare provider to ensure the information displayed on this page applies to your personal circumstances.