Free T4 levels: what's normal, high and low
The active, unbound form of the main thyroid hormone. Confirms thyroid function alongside TSH.
Medically reviewed by Youmna DiStefano, MD · Last reviewed September 2026
The short answer
Free T4 is measured with a standard blood draw; no fasting is needed. A typical reference range is 0.820 – 1.77 ng/dL. At TestWell it's $27.99 all-in as TSH + Free T4, results in 1–3 business days, drawn at Quest or Labcorp. An out-of-range result is a prompt to look closer, not a diagnosis.
- Units
- ng/dL
- Sample
- Blood draw
- Fasting
- Not required
- Results
- 1–3 business days
- Price
- $27.99
- Labs
- Quest or Labcorp · BioReference in NY/NJ
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.
What a high Free T4 means: causes, symptoms, next steps →Usually reflects an underactive thyroid or pituitary issues.
What a low Free T4 means: causes, symptoms, next steps →Educational only — not a diagnosis. Many factors can influence a single result. Discuss anything that concerns you with a healthcare provider.
How do you get a Free T4 test?
Order online, a licensed physician reviews the requisition, and you walk into a nearby lab for the draw. Free T4 is available on its own or inside these panels — panels cost less per marker when you want the fuller picture.
| Option | Includes | Price |
|---|---|---|
| TSH + Free T4 | This marker only | $27.99 |
| Hashimoto's Thyroid Panel | 3 tests | $97.99 |
| Complete Thyroid Panel | 4 tests | $109.99 |
| Women's Health Panel | 8 tests | $129.99 |
| Chronic Fatigue Panel | 9 tests | $169.99 |
Quest vs. Labcorp for Free T4: which lab should you pick?
Both are CLIA-certified national labs and the result is clinically equivalent, so pick whichever location is closer. Your report will print that lab's own reference range, which can differ slightly from the table above.
| Lab | Available | Price |
|---|---|---|
| Quest Diagnostics | Yes | $27.99 |
| Labcorp | Yes | $39.99 |
| BioReference (NY & NJ) | Yes | $24.99 |
Need help choosing a location? Use the lab finder to see draw sites near your ZIP.
Related Thyroid biomarkers
Markers commonly tested alongside Free T4.
Frequently asked
Usually reflects an overactive thyroid or excess thyroid medication. A single result above the reference range is a prompt to look closer with a clinician — often a repeat test and related markers — not a diagnosis on its own.
Ready to test your free t4?
Order in two minutes, get physician-approved, and visit a lab the same day. Starts at $27.99.