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 processing 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 processing 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. Already have results? Analyze them with your AI assistant against our physician-reviewed ranges.
No fasting required.
What can throw off this result
Physician-reviewed “Before your test” pages — what each factor does, for how long, and what to do about it.
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. Full cost breakdown →
| 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 |
| TestWell (drawn at BioReference — New York & New Jersey) | $32.99 | $38.99 | New York and New Jersey orders route to BioReference; Quest Health and Labcorp OnDemand don't take self-ordered draws in those states |
| 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.
Compare more: Quest Diagnostics price list · Labcorp price list · Quest vs Labcorp · Lab test price checker
Most T3 (>99%) is protein-bound and inactive. Free T3 measures the small unbound fraction available to tissues — a more accurate reflection of cellular thyroid activity, especially when binding proteins are altered by pregnancy, estrogen, or liver disease.
Most labs use 2.3-4.2 pg/mL. Levels below the range with normal Free T4 may indicate poor T4-to-T3 conversion (worth checking Reverse T3). Levels above the range with suppressed TSH confirm hyperthyroidism.
Yes when symptoms suggest hyperthyroidism (T3 toxicosis can present with normal T4) or when investigating poor T4-to-T3 conversion. For routine thyroid screening, TSH + Free T4 is sufficient.
On TestWell, Free T3 is $30.99. Quest Direct lists the same test at $40, walk-in hospital labs typically bill $90-120 without insurance.
The CPT code for Free T3 (Triiodothyronine, Free) is 84481. Total T3 is billed separately as 84480.
No fasting required. Draw at consistent time of day for serial monitoring, and at least 4 hours after thyroid medication if on replacement.
Possibly. Some clinicians use the Free T3 / Reverse T3 ratio (target >0.2) to evaluate cellular hypothyroidism in patients with fatigue and normal TSH. Mainstream endocrinology is skeptical; functional medicine often orders both. The Complete Thyroid Panel includes Free T3.
Ordered directly, a Free T3 (Triiodothyronine) test lists at $89.00 at Labcorp OnDemand (prices checked September 2026). TestWell orders the same test at the same Quest or Labcorp patient service centers for $30.99 — $36.99 all-in with the $6 per-order lab processing fee — paid out of pocket at checkout with no insurance, doctor's visit or draw fee; HSA and FSA cards are accepted.
Free T3 (Triiodothyronine) test results are typically ready in 1–3 business days after your draw at Quest or Labcorp. TestWell emails you the moment they post, and your results dashboard shows each marker against its reference range with a plain-English explanation.
Biotin supplements, levothyroxine timing, recent illness and oral contraceptives and estrogen can change a Free T3 (Triiodothyronine) test result without anything being wrong. Biotin supplements can falsely raise Free T3 — stop biotin ≥72 hours before the draw. Levothyroxine timing can raise Free T3 — draw before the dose. Recent illness can shift Free T3 — wait 4–6 weeks after significant illness before judging thyroid. Oral contraceptives and estrogen can raise Free T3 — use TSH and Free T4 — free levels are not affected. Each factor is covered on our physician-reviewed "Before your test" pages; when one applies, the fix is usually to remove it and retest.
Order the Free T3 (Triiodothyronine) test online from TestWell for $30.99 (plus a $6 per-order lab processing fee) — no doctor's visit, referral or insurance needed. A licensed physician authorizes the order, then you walk into any Quest or Labcorp patient service center near you for the draw (the lab locator on our site lists the closest ones by ZIP code), and results arrive in 1–3 business days.
The Free T3 (Triiodothyronine) test is Quest Diagnostics test code 34429, Labcorp test number 010389, BioReference code 0271-7 (CPT 84481). TestWell orders it under those codes for $30.99 at Quest, Labcorp or BioReference — no doctor's visit or insurance required, results in 1–3 business days. Codes verified against the labs' catalogs in 2026.
Medically reviewed by Youmna DiStefano, MD · Last reviewed September 2026
Related guide
TSH vs T4 vs T3: What Each Thyroid Test Measures, Which One to Start With, and How to Read Them Together
Related guide
Blood Tests for Thyroid Symptoms
TestWell Price
$30.99
+ $6 lab processing fee at checkout
No insurance needed · HIPAA compliant
Better value: the Essential Thyroid Panel
Save $31.98This test is part of the Essential Thyroid Panel — 3 tests · 3 biomarkers for $49.99, $31.98 less than à la carte.
$49.99$81.97
3 tests · 3 biomarkers
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Free T3 (Triiodothyronine)
$30.99