When TSH Alone Isn’t Enough: Understanding Free T4
TSH is the standard starting point for checking thyroid function, but it doesn’t always tell the whole story on its own. That’s where Free T4 comes in.
While TSH measures a signal from the brain, Free T4 measures the actual, active thyroid hormone circulating in your blood. Looking at the two together — the signal and the result — gives a doctor a much clearer picture than either alone, especially when TSH results are borderline or don’t match how someone is feeling.
When this test is typically added
- After an abnormal or borderline TSH result
- Alongside TSH from the start, for a fuller initial picture (this is exactly what our Thyroid Check bundle does)
- Monitoring thyroid medication dosing
What to expect
No fasting needed. Biotin supplements can interfere with results, so mention any you’re taking.
Ready to order? The Free T4 (Thyroid Hormone) is $34 at SelectATest, with results in your own secure online portal.
This post is for general information and does not replace advice from your own doctor. Tests are ordered by an independent licensed physician, and results are not a diagnosis. If you are having a medical emergency, call 911.