Quick Facts
- Sample: Blood
- Fasting: No special preparation required; stop high doses of biotin at least 72 hours before testing
- Turnaround: 6-10 days (may take longer based on weather, holiday, or lab delays)
What This Test Measures
This test measures Free T3 (free triiodothyronine), the unbound, biologically active form of the thyroid hormone T3 that circulates in your blood. Most T3 in the body is bound to proteins, but this test isolates and quantifies only the free, unattached portion using equilibrium dialysis combined with LC/MS/MS (liquid chromatography-tandem mass spectrometry) methodology.
This test reports a directly measured, quantitative Free T3 value. It does not measure total T3, T4, TSH, or any thyroid antibody. The dialysis and LC/MS/MS methodology is used specifically to isolate and measure the free hormone fraction with a high degree of analytical specificity.
Benefits
- Measures active, unbound Free T3 using a specific laboratory method
- Uses dialysis and LC/MS/MS for precise Free T3 quantification
- Helps assess thyroid hormone function alongside other clinical information
- Supports evaluation of suspected hyperthyroidism or hypothyroidism
- Can help monitor an existing thyroid condition over time
- Provides objective lab data to discuss with your healthcare provider
Who Is This Test For?
- Individuals with symptoms that may suggest a thyroid disorder
- People whose healthcare provider wants to evaluate Free T3 specifically
- Individuals being monitored for a known thyroid condition
- People whose provider is assessing thyroid hormone status as part of a broader work-up
- Individuals wanting a precise, dialysis-based Free T3 measurement
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 the level of Free T3 (free triiodothyronine) in your blood using dialysis and LC/MS/MS methodology. Free T3 is the unbound, active portion of the T3 hormone. This measurement may help a healthcare provider evaluate thyroid hormone function, though it is one data point and not a standalone diagnostic tool.
2. Who would benefit from this test?
People experiencing symptoms that may be related to thyroid function, or those whose healthcare provider wants to evaluate Free T3 specifically, may benefit from this test. It can also be useful for individuals already being monitored for a thyroid condition.
3. When should I order this test?
You may consider this test if a healthcare provider recommends evaluating your Free T3 level, if you are being monitored for a thyroid condition, or as part of a broader thyroid evaluation directed by your provider.
4. How does this test differ from other thyroid tests?
This test specifically measures Free T3, the unbound form of T3, using dialysis and LC/MS/MS methodology. It does not measure total T3, T4, TSH, or thyroid antibodies. Because it isolates only the free hormone fraction, it provides different information than tests measuring total hormone levels or thyroid antibodies.
5. Do I need to fast before this test?
No special preparation is required for this test. However, you should stop taking high doses of biotin (vitamin B7) at least 72 hours before testing, as biotin can interfere with results.
6. How quickly will I get results?
Results are typically available in 6 to 10 days. This may take longer depending on weather, holidays, or 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, testing timing, and other laboratory results. Free T3 results are often reviewed alongside other thyroid measurements when your provider is evaluating overall thyroid status. A result outside the expected range does not automatically confirm a thyroid condition, and a result within range does not rule one out. Always consult your healthcare provider for interpretation.
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?
If your Free T3 result falls outside the expected range, review it with a qualified healthcare provider. They can help interpret the result in the context of your health history and determine whether additional evaluation is appropriate. Do not start, stop, or change any medication based on this result alone.
9. How often should I get tested?
Testing frequency should be determined by your healthcare provider based on your individual health needs and, if applicable, your thyroid condition. Follow your provider's guidance for retesting as directed.
Pre test preparation
No special preparation is required for this test. Stop taking high doses of biotin (vitamin B7) at least 72 hours before testing, as it can interfere with results.
