Thyroid hormones (TSH, T4)
TSH · free T4 · thyroid test · thyroid blood test
A blood test from a vein for hormones that show how your thyroid gland is working.
For tiredness, weight changes, a racing heart, hair loss, during pregnancy or when planning one, and to check treatment.
⏱ Duration: the blood draw takes 3 to 5 minutes, and results usually take 1 to 3 days
Be sure to tell your doctor
How to prepare
- Time. Morning is best, usually before 10 or 11. Repeat tests should be at about the same time.
- Food. Usually fasting, or a few hours after a light meal. Ask the lab. Water is fine.
- Medicines. Do not stop them on your own. If you take thyroid hormone, ask your doctor whether to take it before or after the test.
- Supplements. Tell your doctor about biotin in advance. You are often asked to stop it 2 to 3 days before the test, but the doctor decides.
What to bring
- Your referral
- Your ID
- Past results and thyroid ultrasound reports, if you have them
How it goes
- You sit down and rest your arm on the armrest
- A band is tied on your arm, and the skin is cleaned with antiseptic
- A quick prick, and blood fills the tube
- The needle is removed, and a cotton pad is pressed on the spot
What you'll feel
- A quick prick
Afterwards
- Press the cotton pad for 3 to 5 minutes
- A doctor explains the result, usually a hormone specialist called an endocrinologist
Common questions
Do I need to fast for a TSH test?
Not strictly, but it is best in the morning and at about the same time. That makes results easier to compare.
Should I take my thyroid pill before the test?
Ask your doctor. Often the pill is taken after the blood draw, so it does not change the result.