Ajax Harwood Clinic
Reverse T3 (rT3)
This test doesn't have a proven medical use for the reasons people usually ask about it.
What this test is
Reverse T3 is a blood test some clinics use to look at thyroid hormone. It is sometimes offered to explain feeling tired or cold, even when normal thyroid tests look fine. No medical guideline recommends checking reverse T3 for this. The level can rise for many normal reasons, like being sick or fasting. A high result does not point to one clear problem. If you feel unwell with a normal TSH, that is worth taking seriously. It is better looked into with tests proven to find real causes, not with reverse T3.
Want to see the full clinical reasoning? The reference we use for this test is open to anyone — it is detailed and written for clinicians, and you are welcome to read it.
Open the clinician reference →Looking for other tests, or more on a condition an ND raised? Explore ask.ajaxharwoodclinic.com →
General health information for Ajax Harwood Clinic patients and the public — not medical advice, and not a substitute for seeing your own doctor. Last reviewed 2026-09-24.