Quick Facts
- Sample: Blood
- Fasting: No fasting required (stop biotin at least 72 hours before collection)
- Turnaround: 1-2 days (may take longer based on weather, holiday, or lab delays)
What This Test Measures
This test measures Free Triiodothyronine (Free T3), the unbound portion of the active thyroid hormone T3 circulating in your bloodstream. Most T3 in your blood is attached to carrier proteins, but the free fraction is what's available to your cells to help regulate metabolism.
Free T3 is a directly measured hormone level, not an antibody, binding protein, or calculated index. Elevated Free T3 can be seen with an overactive thyroid, while low levels can be seen with an underactive thyroid. Factors like your body's conversion of T4 to T3 and the level of carrier proteins in your blood can also influence your results.
Benefits
- Measures active, unbound T3 available to your cells
- Helps evaluate symptoms linked to thyroid function
- Supports follow-up on an already diagnosed thyroid condition
- Provides insight beyond a Total T3 measurement
- Useful for gaining more detail after an abnormal thyroid result
Who Is This Test For?
- People experiencing symptoms of abnormal thyroid function
- Individuals with a previously diagnosed thyroid condition
- Those following up on an abnormal thyroid test result
- People working with a healthcare provider to gain further insight into thyroid symptoms
- Individuals wanting to check current Free T3 levels
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 Free T3, the unbound, active form of triiodothyronine in your blood. It can help a healthcare provider evaluate how much active thyroid hormone is available to your cells for regulating metabolism. This test alone does not diagnose a thyroid condition.
2. Who would benefit from this test?
People experiencing symptoms of abnormal thyroid function, individuals with an already diagnosed thyroid condition, and those following up on a prior abnormal thyroid test result may benefit from this test. It is not intended for every person with thyroid-related symptoms.
3. When should I order this test?
You may consider ordering this test if you have symptoms associated with abnormal thyroid function, if you have an existing thyroid condition you are monitoring, or if a prior thyroid test result was abnormal and further insight is needed. This test does not replace a full medical evaluation.
4. How does this test differ from other thyroid tests?
This test measures Free T3, the unbound and active portion of the hormone, which is directly measured rather than calculated. Some consider it to offer more insight than Total T3, which measures both bound and unbound hormone together. This test does not measure T4, thyroid antibodies, or binding proteins.
5. Do I need to fast before this test?
No fasting is required for this test. You should stop biotin consumption at least 72 hours prior to your collection.
6. How quickly will I get results?
Results are typically available in 1-2 days. Turnaround may take longer due to weather, holidays, or other lab delays.
7. How do I interpret the results?
The meaning of your Free T3 result depends on your individual symptoms, medical history, medications, supplements, and other thyroid-related lab results. Free T3 results are often reviewed alongside other thyroid measurements for a fuller picture. One abnormal result does not automatically confirm a thyroid condition, and one normal result does not rule one out. 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 your results with a qualified healthcare provider, who can help interpret them alongside your symptoms and medical history. Do not stop prescribed medication unless instructed by your healthcare provider. Additional evaluation or testing may be considered based on your provider's guidance.
9. How often should I get tested?
Testing frequency should be based on your individual situation and discussed with your healthcare provider. There is no set schedule for retesting Free T3 levels, and your provider can recommend a plan as directed.
Pre-test preparation
No fasting is required for this test. Stop biotin consumption at least 72 hours prior to the collection. Do not stop prescribed medication unless instructed by your healthcare provider.
