On your lab requisition: Quest “T3 Reverse, LC/MS/MS” (test code 90963)BioReference “Reverse Triiodothyronine Serum/Plasma (rT3)” (test code T397-9)
The short answer
Measures inactive T3 — helps identify thyroid hormone conversion issues and chronic stress effects, measured from a standard blood draw. At TestWell it costs $35.99 plus a $6 lab processing fee, needs no fasting, and results post in 4–7 business days. Physician-authorized with no doctor's visit or insurance needed; draw at Quest or Labcorp.
Hospital Lab
$200
cash pay
Other Labs
$70
+ lab fees
TestWell
$35.99
+ $6 lab processing fee
Reverse T3 (rT3) is an inactive form of T3 that is produced when the body converts T4 to rT3 instead of active T3. This can happen during periods of stress, illness, caloric restriction, or inflammation. High rT3 can cause hypothyroid-like symptoms even when TSH and T4 appear normal. It's particularly useful for evaluating complex thyroid cases.
Measures the inactive 'mirror' form of T3 the body produces under stress, illness, or caloric restriction. High Reverse T3 with normal TSH can indicate cellular hypothyroidism.
Anyone with persistent fatigue, weight gain, and cold intolerance despite normal TSH and Free T4; patients with chronic illness, eating disorders, or stress-related thyroid concerns.
Sample Type
Blood draw
Fasting
Not required
Results In
4–7 business days
Performed At
Quest or Labcorp
Your Reverse T3 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 4–7 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.
A Reverse T3 test costs $35.99 at TestWell — $41.99 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 $200.00 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) | $35.99 | $41.99 | Includes the one $6 lab processing fee, charged once per order |
| TestWell (drawn at BioReference — New York & New Jersey) | $39.99 | $45.99 | New York and New Jersey orders route to BioReference; Quest Health and Labcorp OnDemand don't take self-ordered draws in those states |
| Hospital outpatient lab, self-pay (typical) | $200.00 | $200.00 | Reference figure; hospital charges vary widely by facility and are often higher |
Lab test codes: Quest test code 90963 · Labcorp test no. 070104 · BioReference code T397-9. 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
Reverse T3 is the inactive mirror image of Free T3 — same molecule with iodine atoms swapped. Your body produces it when stressed (illness, surgery, caloric restriction, chronic inflammation) as a brake on metabolism. High rT3 can blunt cellular thyroid activity even when other thyroid labs look normal.
Most labs use 9.2-24.1 ng/dL. Functional clinicians often track the Free T3 / Reverse T3 ratio — values above 0.2 suggest healthy peripheral conversion; below 0.2 suggests blocked conversion (cellular hypothyroidism).
Mainstream endocrinology considers Reverse T3 testing unnecessary — high rT3 is usually a marker of underlying illness, not a treatable problem. Functional medicine uses it for fatigue workup. Order it if you've ruled out other causes of fatigue and want to see if peripheral conversion is impaired.
On TestWell, Reverse T3 is $35.99. Quest Direct lists the same test at $70, walk-in hospital labs typically bill $150-200 without insurance.
The CPT code for Reverse T3 is 84482. Sometimes a payer will require a specific clinical indication (E07.81 or G93.32) to cover it.
Acute or chronic illness, low-calorie diets, intense endurance training, high cortisol, certain medications (amiodarone, beta-blockers, some chemo drugs), and selenium deficiency. Correcting the underlying driver usually normalizes rT3 within 4-8 weeks.
Reverse T3 test results are typically ready in 4–7 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.
No, fasting is not required for a Reverse T3 test — you can eat normally and book any time of day.
Order the Reverse T3 test online from TestWell for $35.99 (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 4–7 business days.
The Reverse T3 test is Quest Diagnostics test code 90963 ("T3 Reverse, LC/MS/MS"), Labcorp test number 070104, BioReference code T397-9 ("Reverse Triiodothyronine Serum/Plasma (rT3)") (CPT 84482). TestWell orders it under those codes for $35.99 at Quest, Labcorp or BioReference — no doctor's visit or insurance required, results in 4–7 business days. Codes verified against the labs' catalogs in 2026.
Medically reviewed by Youmna DiStefano, MD · Last reviewed September 2026
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Better value: the Complete Thyroid Panel
Save $10.97This test is part of the Complete Thyroid Panel — 4 tests · 5 biomarkers for $109.99, $10.97 less than à la carte.
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