TSH and Free T4 Test
A TSH and Free T4 test brings two core thyroid markers together in one order: thyroid-stimulating hormone and free thyroxine. Pairing them lets clinicians view the pituitary signal and the thyroid's output side by side.
About this test
TSH, thyroid-stimulating hormone, is the signal the pituitary gland sends to the thyroid. Free T4 is the unbound, active-available form of thyroxine, the main hormone the thyroid releases.
The test is collected with a routine blood draw at a patient service center, where a phlebotomist takes a sample from a vein in the arm and sends it to the laboratory. People follow any preparation guidance from their ordering clinician.
Who might consider this test?
- Following up on an earlier result
- Exploring symptoms that may be linked to thyroid activity
Test details
| Quest code | 58984 |
|---|---|
| Methodology | Immunoassay |
| Sample type | 1 mL serum |
| Patient preparation | Wait at least 3 days after fluorescein dye angiography before your blood draw. If you are on hemodialysis, wait 2 weeks before your blood draw. |
| Collection | Quest patient service center |
Related tests and panels
Quest resources
Additional details
What pairing these two markers offers
TSH and free T4 describe opposite ends of the same conversation. TSH is the signal the pituitary sends toward the thyroid, while free T4 is the unbound, active-available form of the hormone the thyroid sends back. On its own, either marker tells only half the story; put together, they let a clinician see how the signal going in lines up with the output coming out.
That is why this pairing is a common step beyond a single TSH reading — it adds the hormone side of the picture without expanding to a full panel.
How the two are read as a pair
Because they are meant to be interpreted together, a clinician looks at TSH and free T4 side by side rather than one after the other. The way the two relate can be more informative than either value in isolation. As always, that reading happens in context, with symptoms, history, and any other findings taken into account.
Order online. No doctor's visit and no insurance needed. Your sample is collected at a Quest Diagnostics patient service center.
Laboratory results should always be interpreted by a licensed clinician who knows your health history. This page is information about a test, not medical advice.
Frequently asked questions
What does the TSH and Free T4 test measure?
It measures two markers together: TSH, the pituitary's signal to the thyroid, and free T4, the unbound, active-available form of the thyroid's main hormone.
Why are TSH and free T4 measured together?
TSH reflects the signal going to the thyroid, while free T4 reflects the thyroid's hormone output. Looking at both gives a clinician a fuller view of how the two relate.
How is free T4 different from total T4?
Free T4 measures only the unbound portion of thyroxine, which is less affected by carrier proteins. Total T4 counts both bound and unbound hormone.
How is the sample collected?
With a routine blood draw at a patient service center. A phlebotomist takes a small sample from a vein in the arm and sends it to the laboratory.
Are the two markers read separately?
They are meant to be interpreted together as a pair, in the context of symptoms, history, and the person's overall picture, rather than one on its own.
How much does the TSH and Free T4 test cost?
The test is $50, plus $25 for the doctor's order and Quest blood draw. Total: $75. The $25 fee is waived at $149+. See how ordering works and our blood test cost guide.
Do I need to prepare for this test?
Wait at least 3 days after fluorescein dye angiography before your blood draw. If you are on hemodialysis, wait 2 weeks before your blood draw. This is the preparation Quest publishes for this test; if your clinician gives you different instructions, follow theirs.