The short answer
Measures the active thyroid hormone — important for detecting T4-to-T3 conversion issues, measured from a standard blood draw. At TestWell it costs $30.99 plus a $6 lab fee, needs no fasting, and results post in 1–3 business days. Physician-authorized with no doctor's visit or insurance needed; draw at Quest or Labcorp.
Hospital Lab
$120
cash pay
Other Labs
$40
+ lab fees
TestWell
$30.99
+ $6 lab fee
Free T3 measures the unbound, active form of triiodothyronine, the most potent thyroid hormone. While T4 is produced in larger quantities, T3 is the hormone that actually drives metabolism at the cellular level. This test is especially useful for detecting T4-to-T3 conversion problems, which can cause hypothyroid symptoms even when TSH and T4 are normal.
Measures the unbound (active) form of triiodothyronine — the metabolically dominant thyroid hormone. Used when hyperthyroidism is suspected despite normal Free T4 (T3 toxicosis).
Anyone with hyperthyroid symptoms (palpitations, weight loss, anxiety) but normal TSH/Free T4, monitoring methimazole therapy, evaluating euthyroid sick syndrome, or fine-tuning thyroid replacement.
Sample Type
Blood draw
Fasting
Not required
Results In
1–3 business days
Performed At
Quest or Labcorp
Your Free T3 (Triiodothyronine) results will include values for each of the 1 biomarker tested, along with reference ranges. Results are reviewed by a licensed physician before being released to your secure portal.
If any values fall outside the normal range, your report will include guidance on what that may mean and recommended next steps. You'll receive an email notification when your results are ready, typically within 1–3 business days.
Typical reference range layout
Lab reports show where your value sits relative to established reference intervals—your physician interprets this in context for you.
No fasting required.
A Free T3 (Triiodothyronine) test costs $30.99 at TestWell — $36.99 all-in when ordered alone, because the $6 lab processing fee is charged once per order, with no draw fee or physician fee added. Ordered directly from the labs' own consumer sites, the same test lists at $89.00 at Labcorp OnDemand (list prices checked Sep 12, 2026). Hospital outpatient labs typically bill around $120.00 self-pay for the same test, and often more. With insurance, what you pay depends on your deductible and your plan's negotiated rate; TestWell's price is fixed before the draw and is HSA/FSA-eligible.
| Where you order | Price | One test, all-in | Notes |
|---|---|---|---|
| TestWell (drawn at Quest or Labcorp) | $30.99 | $36.99 | Includes the one $6 lab processing fee, charged once per order |
| Labcorp OnDemand (Labcorp's own site) | $89.00 | $89.00 | list price checked Sep 12, 2026 |
| Hospital outpatient lab, self-pay (typical) | $120.00 | $120.00 | Reference figure; hospital charges vary widely by facility and are often higher |
58% less than the lower lab-direct list price, for the same draw at the same lab. Lab test codes: Quest test code 34429 · Labcorp test no. 010389 · BioReference code 0271-7. Competitor prices are read from the linked public pages and re-checked regularly; the labs' sites may add taxes or change prices without notice.
Related guide
Blood Tests for Thyroid Symptoms
TestWell Price
$30.99
+ $6 lab processing fee at checkout
No insurance needed · HIPAA compliant
Frequently ordered together
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Free T3 (Triiodothyronine)
$30.99