Compare this test’s laboratory options
Reverse T3
Quest Diagnostics1 test optionFrom $46.20
Reverse T3
Quest DiagnosticsCatalog information reviewed: August 24, 2026 by the Sunridge Medical clinical team.
What this laboratory test evaluates
DetailsT3 Reverse, LC/MS/MS – This test measures the levels of 3,3',5'-Triiodothyronine (reverse T3, rT3) in the blood. Reverse T3 is a version of the thyroid hormone that is not active in the body. It's produced from thyroxine (T4), another thyroid hormone. Unlike its counterpart T3, reverse T3 doesn't affect your metabolism. This test is important for understanding thyroid health, especially in conditions where the body is under stress, such as illness, surgery, or malnutrition, which can affect thyroid hormone levels.
What patients is this test right for?This test may be recommended for individuals experiencing symptoms or conditions that could affect thyroid function, including:
• Fasting or malnutrition
• Poorly controlled diabetes mellitus
• Recent trauma or surgery
• Systemic illness
What type of sample is required for this test?0.5 mL serum. A blood draw is necessary.
Additional test information
This test measures the levels of 3,3',5'-Triiodothyronine (reverse T3, rT3) in the blood. Reverse T3 is a version of the thyroid hormone that is not active in the body.
Collection and processing
- Sample type: Serum
- Fasting: No
- Estimated laboratory processing: Results should be available in 2 – 5 business days after the sample is collected
How Sunridge uses laboratory information
Sunridge considers the medical question, symptoms, history, medications, prior results, and whether the finding could change care before recommending testing. A laboratory result is not interpreted in isolation and does not establish a diagnosis by itself.
Before requesting this test
Availability, collection requirements, eligibility, and processing estimates can change. Sunridge reviews each request and, when appropriate, creates the order through Fullscript. Follow the current instructions supplied with the approved order.
Common questions about this laboratory test
- What sample does this test require?
- The listed sample type is Serum. Confirm current collection instructions in the approved order.
- Does this test require fasting?
- The current catalog record lists fasting as: No. Follow the instructions supplied with the approved order.
- How long does laboratory processing usually take?
- Results should be available in 2 – 5 business days after the sample is collected. Timing can change after collection or if a laboratory requires additional review.
About this test
DetailsT3 Reverse, LC/MS/MS - This test measures the levels of 3,3',5'-Triiodothyronine (reverse T3, rT3) in the blood. Reverse T3 is a version of the thyroid hormone that is not active in the body. It's produced from thyroxine (T4), another thyroid hormone. Unlike its counterpart T3, reverse T3 doesn't affect your metabolism. This test is important for understanding thyroid health, especially in conditions where the body is under stress, such as illness, surgery, or malnutrition, which can affect thyroid hormone levels.
What patients is this test right for?This test may be recommended for individuals experiencing symptoms or conditions that could affect thyroid function, including:
• Fasting or malnutrition
• Poorly controlled diabetes mellitus
• Recent trauma or surgery
• Systemic illness
What type of sample is required for this test?0.5 mL serum. A blood draw is necessary.
Additional details
This test measures the levels of 3,3',5'-Triiodothyronine (reverse T3, rT3) in the blood. Reverse T3 is a version of the thyroid hormone that is not active in the body.
Highlighted health areas
- Hormones
- Thyroid
Biomarkers and report focus
The exact analytes and report format can change. Confirm the current contents in the Fullscript order before payment.
- Reverse T3