Reverse T3 (rT3)

ND-recommended test reviewed: reverse T3.
Indications reviewed: no validated primary-care indication identified. TSH result: ____ (date ____).
Not ordered. Rationale discussed: reverse T3 is not recommended by any professional practice guideline; result not reliably interpretable. Ref: Ann Clin Lab Sci 2020 reverse T3 report.
Patient informed test available privately via ND. Patient given info page: https://labs.ajaxharwoodclinic.com/reverse-t3/patient
Revisit if: TSH becomes abnormal, or new symptoms clearly suggest thyroid dysfunction.

Indicated when

None recorded.

Not indicated when

• —Investigating fatigue, 'low T3 syndrome,' or a suspicion that thyroid hormone isn't 'converting' properly [1]
• —Guiding a diagnosis or treatment of 'Wilson's temperature syndrome' or similar labels built around a reverse T3 to free T3 ratio (not a recognized diagnosis; see the thyroid 'low T3' condition page)
• —Routine addition to a thyroid panel alongside TSH, free T4, and free T3 [1]

Why not

A 2020 laboratory-practice audit and recommendation report found that the diagnostic utility of reverse T3 for identifying nonthyroidal illness or guiding treatment is questionable, and that testing for it is not recommended by any professional practice guideline; the same review found that a large share of the rT3 orders it audited were clinically inappropriate [1]. Reverse T3 rises for many non-thyroid reasons, including acute illness, fasting, and normal physiological variation, so an elevated result in an otherwise well person is hard to interpret and does not point to a specific, treatable condition.

Better first step

If fatigue or a 'low thyroid' feeling is the real concern with a normal TSH, look for a non-thyroid cause (sleep, mood, anemia, deconditioning) rather than ordering reverse T3; if genuine central or non-thyroidal illness-related thyroid dysfunction is suspected, that workup rests on TSH and free T4, not rT3 [1].

Typical ND rationale

An ND may order reverse T3 alongside free T3, reasoning that a high reverse T3 to free T3 ratio shows the body is shunting thyroid hormone into an inactive form under stress, which could explain hypothyroid-like symptoms despite normal standard thyroid tests.

Ontario coverage & CONO orderability

OHIP status

uninsured

Reverse T3 does not appear by name anywhere in the 2026 Schedule of Benefits for Laboratory Services (confirmed by a full-text search of the current Schedule PDF), consistent with docs/research/ontario-coverage.md's listing of reverse T3 among tests absent from the community Schedule. Absence from the community Schedule doesn't rule out coverage through a hospital or specialized laboratory pathway, so this is recorded as unverified rather than definitively uninsured. ND-ordered testing is patient-paid regardless (Reg. 552 s.22). Coverage update (reconciliation pass): LifeLabs' Non-OHIP Billable Test List (2025, republished by an Ontario hospital lab) lists this test as patient-paid in community labs. This is secondary evidence, not a ministry statement.

CONO orderable

Yes — CONO list #109

CONO list item 109, blood: 'Reverse T3.'

Linked conditions

• "Low T3" / reverse T3 dominance ↗
• Hypothyroidism ↗

Counselling script

“Reverse T3 isn't recommended by any thyroid guideline I've reviewed, because it goes up for a lot of ordinary reasons and a high result doesn't point to a specific problem we can treat. TSH is the test that actually tells us how your thyroid is working. If you're still feeling unwell, let's look at other explanations together rather than adding this test.”

Revisit if

• —New symptoms clearly suggesting thyroid dysfunction (unexplained weight change, palpitations, heat or cold intolerance, goitre)
• —TSH becomes abnormal on a future test

References

1. [1]Association of Clinical Scientists (Annals of Clinical & Laboratory Science) (2020). Trust your Endocrinologist – Report and Recommendations on the Ordering of Reverse T3 Testing. linkThe diagnostic utility of reverse T3 is questionable and its testing is not recommended by any professional practice guideline; most audited orders were clinically inappropriate
2. [2]American Thyroid Association (2014). Guidelines for the treatment of hypothyroidism: prepared by the American Thyroid Association task force on thyroid hormone replacement. linkolder guidelineNo consistently strong evidence supports non-standard, T3-pathway-focused approaches to thyroid hormone therapy over conventional levothyroxine and TSH-based monitoring
3. [3]LifeLabs (republished by Norfolk General Hospital laboratory) (2025). LifeLabs Non-OHIP Billable Test List (republished by Norfolk General Hospital laboratory, effective 2025). linkListed as a non-OHIP (patient-paid) test at LifeLabs Ontario, 2025