Reverse T3 is a blood test that measures 3,3’,5’-triiodothyronine, an inactive form of thyroid hormone made from T4 when the body slows its metabolism. It rises with illness, calorie restriction, some medicines and higher T4 doses, so practitioners read it as a sign of conversion under stress rather than a diagnosis. Thyroid guidelines do not use it to diagnose or monitor hypothyroidism. Practitioners can add it to a client panel through Vively.
| Test type | Measured in a blood sample |
|---|---|
| Measurements required | Reverse T3, read with TSH, free T4 and free T3 |
| Sample and collection | Blood draw at a collection centre |
| Preparation | No fasting needed. Collect in the morning before any thyroid medication, and avoid crash dieting beforehand. |
| Turnaround | Longer than routine thyroid tests, as not every lab runs it. Your practitioner account shows the expected time. |
| Available through | Add-on test. Add it to any client panel. |
| Pricing | Pricing in your practitioner account |
| Results | Returned in the Vively practitioner platform, beside your client’s other markers |
What are the reverse T3 reference and optimal ranges?
| Typical lab reference | Vively optimal | |
|---|---|---|
| Adults | 230 to 540 pmol/L | 320 to 450 pmol/L |
Some labs report reverse T3 in nmol/L (divide pmol/L by 1,000, so 230 to 540 pmol/L is 0.23 to 0.54 nmol/L) and methods differ, so read results against the range on the client’s report. The optimal band is a follow-up target, not a diagnostic cut-off.
Check a client’s reverse T3 result
Enter the value from your client’s lab report in pmol/L to see where it sits against the typical lab range and the Vively optimal range.
A guide only, not a diagnosis. Read reverse T3 with TSH, free T4, free T3, symptoms and recent intake. Labs differ, so check the result against the range on your client’s report. Nothing you enter is stored or sent.
How do you arrange reverse T3 testing through Vively?
- Get verified. You need to be a verified practitioner to refer tests. Practitioners with a recognised qualification or membership (ATMS, NHAA, ANTA, Dietitians Australia, NSA, CMA or Ahpra registration) can request free practitioner access.
- Add it to a panel. Log in to the practitioner platform and add reverse T3 to a client panel, ideally with TSH, free T4 and free T3 from the same draw. Pricing shows in your account.
- Client collects. Your client collects at a partner collection centre, with their request on their phone or printed.
- Review results. Results come back to you in the practitioner platform, beside your client’s other markers, ready for the follow-up consult.
What does reverse T3 tell you, and what does it not?
Reverse T3 shows how much T4 is being diverted away from active T3. Read it as context for a low free T3. It does not diagnose thyroid disease.
T4 is converted either to active T3 or, by the type 3 deiodinase, to reverse T3, which has no meaningful thyroid hormone activity. More reverse T3 is made, and less is cleared, during illness, fasting and physiological stress.
The American Thyroid Association’s hypothyroidism guideline does not recommend reverse T3 to diagnose or monitor hypothyroidism, and reviews find little evidence that treating a high reverse T3 improves outcomes (Jonklaas et al., 2014; Gomes-Lima and Burman, 2018).
The 320 to 450 pmol/L band is a Vively clinical convention for follow-up, with no published threshold behind it. Use reverse T3 as context for a low free T3, alongside intake, illness and medicines, not on its own.
How should reverse T3 be read with other thyroid markers?
- HighHigh reverse T3, low or low-normal free T3, normal TSH and free T4, recent illness or dieting
Pattern of non-thyroidal illness or low energy availability. Address the cause and retest 6 to 8 weeks later.
- HighHigh reverse T3 with high-normal free T4 on levothyroxine
More T4 means more substrate for reverse T3. Discuss dose and timing with the prescriber rather than reading it as poor conversion.
- HighHigh reverse T3 on amiodarone, glucocorticoids or high-dose propranolol
These medicines reduce T4 to T3 conversion. Note it as a drug effect.
- ContextHigh reverse T3 with low ferritin, low selenium or raised hs-CRP
Iron and selenium support deiodinase activity and inflammation shifts conversion. Correct deficiencies with the GP and retest.
- LowLow reverse T3 with high TSH and low free T4
Less T4 available to convert. This is a hypothyroid pattern and needs GP review.
What can affect a reverse T3 result?
- Calorie restriction, long fasts or very low carbohydrate eating in the weeks before
- Acute or recent illness, surgery, injury or major stress
- Levothyroxine dose and timing, as more T4 means more reverse T3
- Amiodarone, glucocorticoids and high-dose propranolol
- Collection method and units, which differ between labs
When should you refer the client to their GP?
- TSH or free T4 outside the lab range
- Palpitations, tremor, weight loss or heat intolerance with any thyroid result
- A high reverse T3 with missed periods, rapid weight loss or signs of restrictive eating
- A client asking to start or change T3 medication on the basis of reverse T3
How should a client prepare for a reverse T3 test?
Copy or print this to send to your client.
Preparing for your reverse T3 test
- Reverse T3 doesn’t need fasting. If your request also includes glucose or insulin, fast for 8 to 12 hours before a morning collection.
- Eat as you normally do in the week before, and avoid crash dieting or long fasts, which raise reverse T3.
- Pause any biotin supplement (often found in hair, skin and nail formulas) for at least 2 days before your test.
- If you take thyroid medication, have your blood taken before your morning dose and take it straight afterwards, unless your doctor has told you otherwise.
- If you are unwell, tell your practitioner, as illness changes the result. You may be asked to test once you have recovered.
- Take your pathology request to any of 3,700+ collection centres. Bring it printed or on your phone.
- Keep taking prescribed medicines as usual unless your doctor tells you otherwise.
How do practitioners use reverse T3 with clients?
Most useful when free T3 is low or low-normal and the question is why. Order it with TSH, free T4 and free T3 from the same draw, check intake, training load, recent illness and medicines, and use a repeat test 6 to 8 weeks after the cause is addressed to show the change. Use it to track change. It does not justify starting thyroid medication.
Reverse T3 FAQs
Can a naturopath, nutritionist or dietitian order reverse T3 through Vively?
Yes. You need to be a verified practitioner to refer the test. Add it to any client panel on the Vively practitioner platform, ideally with TSH, free T4 and free T3. Pricing shows in your practitioner account. No account yet? Request free access.
Is reverse T3 worth ordering?
Sometimes. It does not diagnose thyroid disease, and guidelines do not use it to monitor hypothyroidism. It earns its place when free T3 is low or low-normal and you want to see whether illness, low intake or medicines are diverting T4 away from active T3, and to track recovery.
What does a high reverse T3 mean?
Usually that the body is conserving energy: during illness, calorie restriction, heavy training or major stress, more T4 becomes reverse T3 and less becomes T3. Higher T4 doses and some medicines also raise it. Read it with TSH, free T4 and free T3, and address the cause before retesting.
What is the free T3 to reverse T3 ratio?
Free T3 divided by reverse T3, used by some practitioners to summarise conversion. The number depends heavily on the units each lab reports, and there is no agreed cut-off, so compare a client against their own earlier results rather than a fixed target.
How long does reverse T3 take to come back?
Longer than routine thyroid tests, because not every lab runs it. Your practitioner account shows the expected turnaround when you add it to a panel.
References
- Jonklaas J, Bianco AC, Bauer AJ, et al. Guidelines for the treatment of hypothyroidism: prepared by the American Thyroid Association task force on thyroid hormone replacement. Thyroid. 2014.
- Gomes-Lima C, Burman KD. Reverse T3 or perverse T3? Still puzzling after 40 years. Cleveland Clinic Journal of Medicine. 2018.
- Peeters RP, Wouters PJ, van Toor H, et al. Serum 3,3’,5’-triiodothyronine (rT3) and 3,5,3’-triiodothyronine/rT3 are prognostic markers in critically ill patients and are associated with postmortem tissue deiodinase activities. Journal of Clinical Endocrinology and Metabolism. 2005.
- Royal College of Pathologists of Australasia. RCPA Manual: thyroid function testing.