What is this test?
Reverse T3 is an inactive metabolite that is formed during the breakdown of thyroxine T4.
Why might it be ordered?
- May be assigned in limited specialized situations to evaluate thyroid hormone turnover.
- For additional information when the endocrinologist determines that the standard tests do not answer the specific question.
What sample is needed?
A healthcare professional collects a venous blood sample. Depending on the method, the laboratory uses serum or plasma.
How should you prepare?
Tell the laboratory about all medicines, hormone treatments, vitamins and supplements you take. Do not stop or change treatment unless your clinician tells you to. Follow any instructions about fasting and the time of collection.
How should you understand the result?
The value may change during severe acute illness, prolonged fasting or undernutrition and other conditions, so it should not be interpreted on its own. Your result is interpreted using the reference interval on the laboratory report and in the context of your symptoms, medical history and other test findings.
Sources and editorial status
This patient-facing text is an editorial draft. It should be approved by a laboratory physician before official publication.