--- title: Free T3 (Triiodothyronine) Test type: test id: free-t3 url: "https://www.test-well.com/tests/free-t3" price_usd: 30.99 lab_fee_usd: 6 all_in_usd: 36.99 cpt: 84481 category: Thyroid sample: Blood draw fasting_required: false results_in: "1–3 business days" labs: - Quest - Labcorp - BioReference orderable: true reviewed_at: 2026-09-14 order_url: "https://www.test-well.com/cart?add=free-t3&utm_source=ai_agent&utm_medium=markdown" --- # Free T3 (Triiodothyronine) Test > 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. ## Key facts | Fact | Value | | --- | --- | | Price | $30.99 + $6 lab processing fee per order ($36.99 all-in for this test alone) | | CPT code | 84481 | | Sample | Blood draw | | Fasting | Not required | | Results | 1–3 business days | | Labs | Quest Diagnostics, Labcorp, BioReference (NY & NJ) | | Biomarkers measured | 1 | | Physician authorization | Included — no doctor's visit, referral or insurance needed | | Payment | Card, HSA or FSA; cash-pay only (no insurance billing) | ## What does the Free T3 (Triiodothyronine) test tell you? Measures the active thyroid hormone — important for detecting T4-to-T3 conversion issues. 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. **Clinical use:** Measures the unbound (active) form of triiodothyronine — the metabolically dominant thyroid hormone. Used when hyperthyroidism is suspected despite normal Free T4 (T3 toxicosis). ## Who should order it? 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. ## Biomarkers measured - [Free T3](https://www.test-well.com/biomarkers/free-t3) ## Price by lab | Lab | Test price | All-in (with $6 fee) | Notes | | --- | --- | --- | --- | | Quest Diagnostics | $30.99 | $36.99 | Choose at checkout; walk-in patient service centers nationwide (not NY/NJ) | | Labcorp | $30.99 | $36.99 | Choose at checkout; walk-in patient service centers nationwide (not NY/NJ) | | BioReference (NY & NJ) | $32.99 | $38.99 | New York and New Jersey orders route here automatically | Rhode Island is not served. Prices are identical online and in the lab; no draw fee or physician fee is added. ## How much does a Free T3 (Triiodothyronine) test cost? 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 2026-09-12](https://www.ondemand.labcorp.com/lab-tests/free-t3-test) | | Hospital outpatient lab, self-pay (typical) | $120.00 | $120.00 | Reference figure; hospital charges vary widely by facility and are often higher | Lab test codes: Quest test code 34429 · Labcorp test no. 010389 · BioReference code 0271-7. ## How do you prepare? No fasting required. ## Related conditions - [Hyperthyroidism](https://www.test-well.com/conditions/thyroid-problems) (E05.90) - Graves disease (E05.00) - T3 toxicosis (E05.90) - Euthyroid sick syndrome (E07.81) ## Common questions about the Free T3 (Triiodothyronine) test ### Why measure Free T3 instead of Total T3? 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. ### What's a normal Free T3 level? 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](https://www.test-well.com/tests/reverse-t3)). Levels above the range with suppressed TSH confirm hyperthyroidism. ### Should I order Free T3 with TSH and Free T4? 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](https://www.test-well.com/tests/tsh-with-free-t4) is sufficient. ### How much does a Free T3 test cost without insurance? 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. ### What is the CPT code for Free T3? The CPT code for Free T3 (Triiodothyronine, Free) is 84481. Total T3 is billed separately as 84480. ### Do I need to fast? No fasting required. Draw at consistent time of day for serial monitoring, and at least 4 hours after thyroid medication if on replacement. ### Should I add Free T3 + Reverse T3 to investigate fatigue? 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](https://www.test-well.com/tests/thyroid-complete-panel) includes Free T3. ## How to order 1. Add to cart: https://www.test-well.com/cart?add=free-t3&utm_source=ai_agent&utm_medium=markdown 2. Create an account or sign in, confirm your state and preferred lab, pay by card, HSA or FSA. 3. A licensed physician authorizes the order (usually within minutes); the requisition arrives by email. 4. Walk into any Quest Diagnostics, Labcorp, BioReference (NY & NJ) patient service center — no appointment needed at most sites. 5. Results post to your TestWell portal in 1–3 business days with reference ranges and flags. ## Related - [Blood Tests for Thyroid Symptoms](https://www.test-well.com/guides/blood-tests-for-thyroid-symptoms) - [Hashimoto's Thyroid Panel](https://www.test-well.com/tests/hashimotos-thyroid-panel) — 3 tests · $97.99 - [Essential Thyroid Panel](https://www.test-well.com/tests/essential-thyroid-panel) — 3 tests · $49.99 - [Complete Thyroid Panel](https://www.test-well.com/tests/thyroid-complete-panel) — 4 tests · $109.99 - [Free T4 (Thyroxine)](https://www.test-well.com/tests/free-t4-test) — $23.99 - [Reverse T3](https://www.test-well.com/tests/reverse-t3) — $35.99 - [T3 Uptake](https://www.test-well.com/tests/t3-uptake-test) — $22.99 - [T3, Total (Triiodothyronine)](https://www.test-well.com/tests/total-t3-test) — $24.99 - [Thyroglobulin Antibodies](https://www.test-well.com/tests/thyroglobulin-antibodies) — $26.99 - [All Thyroid tests](https://www.test-well.com/tests/category/thyroid) - [Full test directory](https://www.test-well.com/tests/directory) --- Medically reviewed by Youmna DiStefano, MD (Medical Reviewer, TestWell); last reviewed 2026-09-14. Review policy: https://www.test-well.com/reviewers/youmna-distefano-md Canonical page: https://www.test-well.com/tests/free-t3 Machine-readable catalog: https://www.test-well.com/api/catalog.json · MCP server: https://www.test-well.com/mcp · Overview for agents: https://www.test-well.com/llms.txt Prices are cash-pay, in USD, and include physician authorization; every order adds one flat $6 lab processing fee. Educational content is not a diagnosis — discuss results with a clinician.