Reverse T3 (rT3) Test
A Reverse T3 test measures reverse T3, or rT3, an inactive form of thyroid hormone the body produces from T4. It is a specialized and less commonly ordered test that some clinicians use to add detail to a thyroid picture.
About this test
When the body processes T4, it can convert it into T3, the more active thyroid hormone, or into reverse T3, an inactive counterpart. Reverse T3 does not carry out the active work that T3 does, and its production can rise in certain circumstances.
The test uses a routine blood draw at a patient service center, where a phlebotomist collects a sample from a vein in the arm and sends it to the laboratory. People follow any preparation guidance from their ordering clinician.
Test details
| Quest code | 90963 |
|---|---|
| Methodology | Chromatography/Mass Spectrometry |
| Sample type | 0.5 mL serum |
| Collection | Quest patient service center |
Reference range
8-25 ng/dL
Reference ranges are general guidance. The range printed on your own laboratory report is the one that applies to your result.
Related tests and panels
Quest resources
Additional details
A specialized, less common marker
Reverse T3 is not part of a standard first look at the thyroid. When the body handles T4, it can route it toward the active hormone, T3, or toward reverse T3, an inactive counterpart that does not carry out the same work in tissues. This test measures how much of that inactive form is circulating.
Because it sits outside the usual panel of thyroid markers, reverse T3 is generally ordered deliberately, when a clinician has a particular question in mind rather than as a routine check.
How clinicians tend to use it
Reverse T3 is most often a follow-on marker, considered after more common thyroid tests have already been reviewed. A single specialized value is not designed to stand alone, so a clinician looks at it in combination with markers like TSH, free T4, and free T3, along with symptoms and history, to see what it adds to the overall picture.
What to expect and how results are read
Having the sample collected is the same simple process as any other blood test: a phlebotomist collects the sample, and a phlebotomist draws a small amount from a vein in the arm during a short visit at a patient service center. Results are posted to the account once the laboratory reports them, and a clinician interprets this specialized marker in context rather than in isolation. Given how selectively it is ordered, the value of the result really comes from how it fits with the other thyroid findings a clinician is already weighing.
Order online and a physician order is included — no doctor's visit and no insurance needed. Your sample is collected at a Quest Diagnostics patient service center.
Laboratory results should always be interpreted by a licensed clinician who knows your health history. This page is information about a test, not medical advice.
Frequently asked questions
What does the Reverse T3 test measure?
It measures reverse T3, an inactive form of thyroid hormone that the body makes from T4. Unlike T3, reverse T3 does not carry out the active hormone work in tissues.
How is reverse T3 different from T3?
T3 is the active thyroid hormone that tissues use, while reverse T3 is an inactive counterpart the body also produces from T4. They come from the same source but play different roles.
Is reverse T3 a common test?
No. It is a specialized, less commonly ordered marker, usually chosen when a clinician has a specific reason to look at it rather than as part of a routine thyroid evaluation.
How is the sample collected?
With a standard blood draw at a patient service center. A phlebotomist takes a small sample from a vein in the arm and sends it to the laboratory.
Is reverse T3 read on its own?
It is generally interpreted alongside other thyroid markers and the person's overall situation, since a single specialized value is not meant to stand alone.
How much does the T-3 Reverse test cost?
The cash price at Celio Health is $95. That covers the physician's order and sample collection at a Quest patient service center — no insurance is needed and there's no separate doctor's visit to pay for.