--- title: Free T4 (Thyroxine) Test type: test id: free-t4 url: "https://www.test-well.com/tests/free-t4-test" price_usd: 23.99 lab_fee_usd: 6 all_in_usd: 29.99 cpt: 84439 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-t4-test&utm_source=ai_agent&utm_medium=markdown" --- # Free T4 (Thyroxine) Test > Measures free (unbound) T4 — the primary hormone produced by the thyroid gland, measured from a standard blood draw. At TestWell it costs $23.99 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 | $23.99 + $6 lab processing fee per order ($29.99 all-in for this test alone) | | CPT code | 84439 | | 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 T4 (Thyroxine) test tell you? Measures free (unbound) T4 — the primary hormone produced by the thyroid gland. Free T4 (thyroxine) is the unbound, biologically active form of the primary thyroid hormone. It is converted to T3 (the more active form) in tissues throughout the body. Free T4 is the most reliable marker of actual thyroid hormone production because it is not affected by changes in binding proteins. Elevated Free T4 suggests hyperthyroidism, while low levels indicate hypothyroidism. This test is most useful when ordered alongside TSH for a complete picture of thyroid function, but can also be ordered standalone to monitor patients on thyroid medication. **Clinical use:** Measures the unbound (active) form of thyroxine. Pairs with TSH to confirm thyroid dysfunction and distinguish primary from central causes. ## Who should order it? Anyone with abnormal TSH, fatigue, weight changes, hair thinning, cold intolerance, or other symptoms of thyroid disease. Monitoring patients on levothyroxine or methimazole therapy. ## Biomarkers measured - [Free T4](https://www.test-well.com/biomarkers/free-t4) ## Price by lab | Lab | Test price | All-in (with $6 fee) | Notes | | --- | --- | --- | --- | | Quest Diagnostics | $23.99 | $29.99 | Choose at checkout; walk-in patient service centers nationwide (not NY/NJ) | | Labcorp | $23.99 | $29.99 | Choose at checkout; walk-in patient service centers nationwide (not NY/NJ) | | BioReference (NY & NJ) | $24.99 | $30.99 | 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 T4 (Thyroxine) test cost? A Free T4 (Thyroxine) test costs $23.99 at TestWell — $29.99 all-in when ordered alone, because the $6 lab processing fee is charged once per order, with no draw fee or physician fee added. Hospital outpatient labs typically bill around $150.00 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) | $23.99 | $29.99 | Includes the one $6 lab processing fee, charged once per order | | Hospital outpatient lab, self-pay (typical) | $150.00 | $150.00 | Reference figure; hospital charges vary widely by facility and are often higher | Lab test codes: Quest test code 866 · Labcorp test no. 001974 · BioReference code 0091-9. ## How do you prepare? No fasting required. If on thyroid medication, take your dose after the blood draw. ## Related conditions - [Hypothyroidism](https://www.test-well.com/conditions/thyroid-problems) (E03.9) - [Hyperthyroidism](https://www.test-well.com/conditions/thyroid-problems) (E05.90) - Hashimoto thyroiditis (E06.3) - Graves disease (E05.00) ## Common questions about the Free T4 (Thyroxine) test ### Why measure Free T4 instead of Total T4? Most T4 (>99%) is protein-bound to thyroid-binding globulin and inactive. Free T4 measures the small unbound fraction available to tissues — a more accurate reflection of thyroid hormone activity, especially in pregnancy, on estrogen, or with liver disease (all of which alter binding proteins). ### What's a normal Free T4 level? Most labs use a range of about 0.8-1.8 ng/dL. Low Free T4 with elevated [TSH](https://www.test-well.com/tests/tsh) confirms primary hypothyroidism. Elevated Free T4 with suppressed TSH confirms hyperthyroidism. ### Should I get Free T4 with TSH or instead of it? With it. [TSH](https://www.test-well.com/tests/tsh) is the screening test; Free T4 confirms the diagnosis when TSH is abnormal. The [TSH + Free T4](https://www.test-well.com/tests/tsh-with-free-t4) bundle is the standard pairing for full thyroid evaluation. ### How much does a Free T4 test cost without insurance? On TestWell, Free T4 is $23.99. Quest Direct lists the same test at $40, walk-in hospital labs typically bill $100-150 without insurance. Same CLIA-certified labs, same biomarker — TestWell just removes the markup. ### What is the CPT code for a Free T4 test? The CPT code for Free T4 (direct measurement) is 84439. Total T4 is billed as 84436. Most thyroid workups bill 84443 (TSH) + 84439 (Free T4) together. ### Do I need to fast for a Free T4 test? No fasting required. Try to draw at the same time of day for serial monitoring, and at least 4 hours after your levothyroxine dose if you're on thyroid replacement therapy. ## How to order 1. Add to cart: https://www.test-well.com/cart?add=free-t4-test&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 - [Essential Thyroid Panel](https://www.test-well.com/tests/essential-thyroid-panel) — 3 tests · $49.99 - [Advanced Thyroid Panel](https://www.test-well.com/tests/advanced-thyroid-panel) — 7 tests · $129.99 - [General Wellness Advanced Panel](https://www.test-well.com/tests/whole-body-essentials-panel) — 14 tests · $209.99 - [Free T3 (Triiodothyronine)](https://www.test-well.com/tests/free-t3) — $30.99 - [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-t4-test 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.