Free T4 Test
The active, unbound form of the main thyroid hormone. Confirms thyroid function alongside TSH.
What is Free T4?
The active, unbound form of the main thyroid hormone. Confirms thyroid function alongside TSH.
Free T4 Reference Range
These are the typical adult reference ranges used by major US labs. Your report will include the specific range used by the lab that processed your sample.
| Population | Range |
|---|---|
| age 18+ | 0.820 – 1.77 ng/dL |
Reference ranges are educational. Always interpret your result with the specific range printed on your lab report and discuss anything outside the range with a clinician.
What your Free T4 result may mean
Usually reflects an overactive thyroid or excess thyroid medication.
Usually reflects an underactive thyroid or pituitary issues.
Educational only — not a diagnosis. Many factors can influence a single result. Discuss anything that concerns you with a healthcare provider.
Sources
Related Thyroid biomarkers
Markers commonly tested alongside Free T4.
Frequently asked
No. TestWell's licensed physician network reviews and approves your order — usually within minutes. You can place an order online without an in-person visit or a referral from your own doctor.
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