Total Reverse T3 (Thyroxine) – Serum or Plasma Mass Concentration
This test measures the total amount of reverse triiodothyronine (rT3) in your blood. Reverse T3 is a form of thyroid hormone that is less active than the main thyroid hormones.
["Reverse T3 helps balance thyroid hormone levels but isn’t directly linked to thyroid function."]
Key facts at a glance
- LOINC
- 3052-8
- Short code
- T3Reverse SerPl-mCnc
- Synonyms
- T3Reverse SerPl-mCnc
- Category
- chemistry
- Sample
- serum
- Container
- Red-top tube (SST)
- Units
- N/A
- Ref low
- 80
- Ref high
- 200
- Critical range
- 20 N/A – 400 N/A
- Fasting
- false
- Population
- adult
- Sex
- all
- Age range
- 18–65 years
- CPT
- 84436
- SNOMED
- 302346007
- Specimen volume
- 5 mL
- Stability
- Room temperature: 4h, Refrigerated: 24h, Frozen: 7d
- Hemolysis max
- 500
- Lipemia max
- 1000
- Icterus max
- 500
- TAT
- 4–24 hours
- Order
- routine
What Is Reverse T3?
Reverse T3 (rT3) is a metabolite of the thyroid hormone triiodothyronine (T3). Normally, your body converts T3 into rT3 for storage or excretion. While rT3 is not the primary thyroid hormone, it can influence how your body responds to thyroid medications or conditions affecting thyroid metabolism.
Why Might You Need This Test?
Your doctor may order a reverse T3 test if you have symptoms of thyroid dysfunction (like fatigue, weight changes, or mood swings) but your standard thyroid tests (such as TSH, free T3, or free T4) are within normal ranges. It can also be checked in cases of thyroid hormone resistance or certain metabolic disorders.
How Is the Test Done?
A blood sample is drawn from a vein in your arm. The sample is sent to a lab where it is analyzed to measure the total rT3 concentration. Results are reported in mass concentration units (often expressed as nanograms per deciliter, ng/dL).
What Do the Results Mean?
High levels of reverse T3 may suggest conditions like stress, liver disease, or certain medications that interfere with thyroid hormone metabolism. Low levels are less commonly evaluated but could be associated with rare metabolic or genetic factors. Your doctor will interpret results in the context of your overall health and other tests.
Reference range
Adult: 80-200 ng/dLN/A
Take your thyroid medication after the blood draw if applicable. No fasting required.
Clinical interpretation
How abnormal results are interpreted and what conditions they suggest.
◆Associated findings1
Short name
Total Reverse T3
Frequently asked questions
What causes elevated reverse T3 levels?
Can low reverse T3 levels affect thyroid health?
Does reverse T3 testing help diagnose thyroid disease?
Sources
- 1
- 2Lab Tests OnlineSource
- 3
Click any link to access the full source. PubMed Central (PMC) links provide free full-text access.
This information is for educational purposes only and is not a substitute for professional medical advice, diagnosis, or treatment.
This content is for general informational and educational purposes only and is not a substitute for professional medical advice, diagnosis, or treatment. Always seek the guidance of a qualified healthcare provider with any questions you have about a medical condition, and never disregard professional medical advice or delay seeking it because of something you read here.
If you think you may have a medical emergency, call your local emergency number or go to the nearest emergency department immediately.
Medically reviewed by WellAlly Editorial Team Last reviewed August 17, 2026. · Read our editorial policy