Quick Facts
- Sample: Blood
- Fasting: No special preparation required
- Turnaround: 8-9 days (may take longer due to weather, holiday, or lab delays)
What This Test Measures
This test measures Reverse T3 (RT3), the inactive form of triiodothyronine (T3), using LC/MS/MS methodology on a serum sample. RT3 is directly measured, not calculated, and reflects one specific pathway in thyroid hormone metabolism rather than a full picture of thyroid function.
Your body normally converts thyroxine (T4) into active T3 and inactive RT3 in balanced ratios. Certain conditions, including significant physical stress, serious illness or injury, and use of drugs like amiodarone or glucocorticoids, can shift more T4 conversion toward RT3. Because stress alone can raise RT3, this single result is not on its own indicative of a thyroid condition.
Benefits
- Measures reverse T3, a byproduct of T4 to T3 conversion
- Helps flag stress-related shifts in thyroid hormone metabolism
- Uses LC/MS/MS methodology for precise lab measurement
- Provides one data point for broader metabolic evaluation
- Can add context when reviewed alongside other thyroid results
Who Is This Test For?
- People experiencing prolonged physical or emotional stress
- Those recovering from serious illness, injury, or surgery
- Individuals managing insulin-dependent diabetes
- People with liver or kidney disease
- Those with chronic alcohol use or certain nutrient deficiencies
- Anyone working with a provider on metabolic health questions
How It Works
- Order Your Test Online
- Visit a Local Lab
- Get Results Online
FAQ
1. What is the purpose of this thyroid test?
This test measures Reverse T3 (RT3), the inactive form of T3, in your blood using LC/MS/MS methodology. It helps a healthcare provider evaluate whether stress, illness, or other factors may be affecting how your body converts thyroid hormone. It is not a comprehensive thyroid panel and does not directly confirm thyroid function on its own.
2. Who would benefit from this test?
This test may be useful for people under significant stress, those recovering from illness, injury, or surgery, individuals managing insulin-dependent diabetes, or those with liver or kidney disease. It can also be relevant for people with chronic alcohol use or certain nutrient deficiencies who are exploring metabolic factors with a healthcare provider.
3. When should I order this test?
You might consider this test during periods of prolonged stress, after a serious illness, injury, or surgery, or when working with a provider to understand factors affecting thyroid hormone conversion. This test does not diagnose a condition and does not provide a complete thyroid assessment on its own.
4. How does this test differ from other thyroid tests?
This test measures RT3, a directly measured hormone level reflecting inactive T3, rather than active thyroid hormone levels, thyroid antibodies, or binding proteins. Because RT3 can rise from stress alone, some providers evaluate it alongside a Free T3 test to compare the ratio between the two. This test does not provide the same information as TSH, T4, thyroid antibody, or binding protein testing.
5. Do I need to fast before this test?
No special preparation is required for this test.
6. How quickly will I get results?
Results are typically available in 8-9 days. Results may take longer based on weather, holiday, or lab delays.
7. How do I interpret the results?
The meaning of your RT3 result depends on your individual health history, current stress levels, medications, and other lab results. RT3 results are often considered alongside other thyroid measurements, such as Free T3, for added context. An elevated or low result does not confirm or rule out a thyroid condition on its own. Discuss your results with a qualified healthcare provider.
Disclaimer: Reference ranges may vary by laboratory. Listed ranges are general guidelines and may differ from those used by the performing lab. Always consult your healthcare provider for interpretation.
8. What should I do if my results are abnormal?
Review any abnormal result with a qualified healthcare provider. They can help determine whether additional evaluation or testing may be appropriate based on your health history and other lab results. Do not stop prescribed medication unless instructed by your healthcare provider.
9. How often should I get tested?
Testing frequency should be determined as directed by your healthcare provider, based on your individual health circumstances and reason for testing.
Pre-test preparation
No special preparation required. Do not stop prescribed medication unless instructed by your healthcare provider.
