Reverse T3
Reverse T3 is an inactive metabolite of T4 produced by alternative deiodination. Levels rise during severe illness, calorie restriction, trauma, and chronic stress and may reflect a shift away from active T3 production. High reverse T3 with low or normal free T3 is sometimes called euthyroid sick syndrome and usually resolves with recovery.
Optimal range: who says what
No institution or named practitioner we track states an optimal target for Reverse T3. How we verify ranges.
- General guidance, no named sourceLower half of referenceHigh rT3 with low-normal free T3 suggests impaired T4-to-T3 conversion under illness or caloric stress
- Lab reference interval9.2-24.1 ng/dLWhat a lab report flags against. A lab interval is not an optimal target.
4 providers include this
Thyroid Function
Why Reverse T3 matters
Elevated during stress, illness, or caloric restriction. High levels despite normal TSH/T4 may explain persistent fatigue and metabolic issues. Indicates thyroid hormone conversion problems.
Which Providers Test Reverse T3?
Function Health is both the cheapest ($365/year) and the most comprehensive (160+ biomarkers) panel that includes Reverse T3.
4 panels that include it, cheapest first
| Provider | Annual Cost | Total Biomarkers | $/Biomarker |
|---|---|---|---|
 Function Health | $365 | 160+ | $2.28 |
| $700 | 138 | $5.07 | |
| $895 | 100+ | $8.95 | |
| $1950 | 130+ | $15.00 |
$/Biomarker is annual cost divided by the panel's advertised biomarker count, not the price of this one test. We track 23 blood test providers (32 plans); 21 of those plans are itemized marker by marker. Compare all of them.
17 itemized panels do not include Reverse T3
Superpower · WHOOP Advanced Labs · Labcorp OnDemand · Life Extension Elite · Everlywell · Mito Health · InsideTracker · Marek Health Base · Marek Health Comprehensive · Blueprint · Empirical Health · Oura Health Panels · SiPhox Health · Hims Labs · Healthspan · Vitality Blueprint Standard · Ultrahuman Blood Vision Annual
11 providers not itemized in our matrix
We have not itemized these marker by marker (some sell tests one at a time), so this page cannot say whether they offer Reverse T3. Check with them directly.
Life Extension Standard · Quest Health · Ultrahuman Blood Vision · Lifeforce · Hundred Health · Personalabs · Walk-In Lab · HealthLabs · WHOOP Specialized Panels · Marek Health Essential · Vitality Blueprint Upload
Experts discussing Reverse T3
Podcast episodes where clinicians and researchers cover this marker in depth. Curated by hand; an episode is listed only when the marker is a substantial topic, not a passing mention.
- Is Your Thyroid the Hidden Root Cause of Your Health Issues?Disclosure: Hyman co-founded Function Health, which appears in our blood-test comparisons.
- The Hidden Epidemic of Low Thyroid FunctionDisclosure: Hyman co-founded Function Health, which appears in our blood-test comparisons.
Frequently Asked Questions
What is the optimal range for Reverse T3?
No institution or named practitioner we track states an optimal target for Reverse T3. General guidance without a named source: Lower half of reference (High rT3 with low-normal free T3 suggests impaired T4-to-T3 conversion under illness or caloric stress). Lab reference interval: 9.2-24.1 ng/dL. That is what a lab report flags against, not an optimal target.
Which blood test providers include Reverse T3?
4 of the 21 blood testing panels we itemize marker by marker include Reverse T3 in their panels. This biomarker has limited availability.
Related: YouBoost rates lifestyle and supplement interventions by evidence.
Medical Disclaimer
This information is for educational purposes only and is not medical advice. Always consult with a qualified healthcare provider about your specific health needs.
Last reviewed Aug 26, 2026 · First published Nov 30, 2025