Reverse T3 Test
This page explains the reverse t3 test, what it measures, and how to arrange it. A reverse T3 test measures the amount of reverse T3, an inactive form of thyroid hormone, in a blood sample. It is usually ordered when a person has thyroid symptoms that do not match their other thyroid test results, or when a clinician is evaluating how the body converts thyroid hormone.
- Sample type
- blood
- Category
- Thyroid
- Turnaround
- 1-3 business days
- Price
- $118
- Referral
- Not required
A reverse T3 test measures the amount of reverse T3, an inactive form of thyroid hormone, in a blood sample. It is usually ordered when a person has thyroid symptoms that do not match their other thyroid test results, or when a clinician is evaluating how the body converts thyroid hormone.
What it measures
- Reverse T3 — The main hormone measured; it is an inactive form of T3.
- Total T3 — Often checked alongside reverse T3 to compare active and inactive hormone levels.
- Free T4 — A storage form of thyroid hormone that the body converts into T3 or reverse T3.
- TSH — A pituitary signal that helps show whether the thyroid is being stimulated.
- Free T3 — The active thyroid hormone that affects energy, temperature, and metabolism.
Who it is for
A clinician such as an endocrinologist, primary care doctor, or other licensed provider may order this test when thyroid symptoms persist despite normal standard thyroid tests. It is not a routine screening test.
Preparation
No fasting is usually required. Tell your clinician about all medications, supplements, and recent illness, because these can affect thyroid hormone levels.
Results and what they mean
Results are reported as a numeric level for reverse T3 and any other markers tested, along with the laboratory's reference range. A clinician interprets these numbers together with your symptoms, history, and other thyroid tests. This is general information only and is not medical advice; discuss your results with a qualified healthcare professional.
How to order this test
- Choose the test and place a confidential order online.
- Select a certified collection site and pick a time that suits you.
- Have your specimen collected — most draws take only a few minutes.
- Review results in a secure portal, typically within 1–3 days.
Preparation, hours, and pricing vary by site; confirm details directly with the lab before your visit.
Availability by state
Direct-access online ordering for the reverse t3 test is available in most states. It is currently unavailable in 6 states:
Everywhere else you can order confidentially and collect your sample at a certified site. Browse by state →
Frequently asked questions
Do I need to fast for a reverse T3 test?
No. Fasting is not normally required for this blood test.
Can I take my thyroid medication before the test?
Ask your clinician. Some medications may need to be timed differently, but do not stop or change any medication without medical advice.
How long until results are ready?
Results are typically available within 1 to 3 business days, though this can vary by laboratory.
Is a high reverse T3 always a problem?
No. Reverse T3 levels can rise with stress, illness, or dieting. Only a clinician can interpret what your result means for you.