Good to knowOne result rarely tells the whole story. Your provider looks at your results together with your symptoms, exam, and other tests.
What the test is
It's less useful for underactive thyroid.
Why it's done
- Low TSH with normal free T4
- Following an overactive thyroid
Getting ready and what happens
- Ask about stopping biotin 2 to 3 days before.
How the test is done
- A health worker cleans the skin, puts a band around your arm, and draws blood from a vein with a small needle. It takes a few minutes.
What the results mean
High
Points to an overactive thyroid.
Questions to ask your provider
- What do my results mean for me?
- Do I need to repeat this test or have other tests?
Risks
A blood draw is very safe. You may have slight pain or a small bruise where the needle went in.
Related conditions
Related medicines
Related tests
Sources
Last updated 2026-11-13.