Free Triiodothyronine (FT3) (LC/MS)
Diagnostic Blood Test:
- Free Triiodothyronine (FT3) (LC/MS)
Free Triiodothyronine or FT3 is the active thyroid hormone. Its job is to regulate metabolism, body temperature, and heart rate. Optimal levels of FT3 support healthy insulin sensitivity, muscle growth, fat loss, brain function, and mood. Measuring FT3 levels can help detect hyperthyroidism (an overactive thyroid) or hypothyroidism (an underactive thyroid).
is a measure of unbound Triiodothyronine (T3) that is available to the body’s tissues.
Direct measurement of FT3 by equilibrium dialysis, high-pressure liquid chromatography, and tandem mass spectrometry provides enhanced accuracy over commonly used analog methods and is not affected by clinical conditions that impact protein binding capacity. Examples of clinical conditions in which the FT3 by the LC/MS method may be preferred include congenital absence of thyroxine-binding protein (TBG), pregnancy, administration of oral contraceptives or hormone therapy, administration of atypical antipsychotic medications, malignancy or other critical illnesses.
Pairs well with
Free Triiodothyronine (FT3) (LC/MS)
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How it works
Purchase your tests
Purchase this test and any other tests you'd like online. A healthcare provider will review and approve your test requests; no healthcare provider visit is required.
Provide your sample
Visit a Labcorp location near you for sample collection. Use our Labcorp locator below to find a location near you.
Get your results
Our partnered facilities will process your bloodwork. Lab Results typically arrive within 14 business days, and we will email them to you as soon as they arrive.
Lab work FAQs
Please read our FAQs page to find out more.
How quickly will my lab results arrive?
Your lab results will typically arrive within two weeks, though processing time may vary based on the size and complexity of your panel. Rest assured, once your results are ready, they will be securely delivered to your email. No waiting rooms. No chasing paperwork. Just precision diagnostics at your fingertips.
Does Marek Diagnostics accept insurance?
Marek Diagnostics is a cash-pay service. Our platform offers direct access to comprehensive testing without the limitations, denials, or delays imposed by insurance companies. If traditional insurance covered the kind of proactive, high-quality lab work we offer, Marek Diagnostics wouldn’t need to exist.
However, many clients successfully use their HSA/FSA to cover their testing costs. Marek Diagnostics is partnered with TrueMed for convenient deployment of HSA/FSA funds at checkout.
My panel Meets Treatment Requirements — what does that mean?
Marek Diagnostics is an extension of Marek Health, the leading health optimization platform designed to turn your results into informed action.
If your panel Meets Treatment Requirements, you’re eligible to enroll into Guided Optimization, an exclusive program that connects you with:
- Detailed, expert led lab analysis
- A consultation with a Marek Health coach and board-certified medical provider
- A precision health optimization plan
- Access to high-quality treatment options
If you’re unsure what to do with your results, Marek Health is the bridge between lab results and achieving your goals.
Do I need to pay a separate fee at the lab to get my blood drawn?
No additional payment is required at the lab. Our expert-built panels include the venipuncture and if you’re building a custom panel or testing biomarkers individually, a $5 venipuncture fee will be automatically added at checkout.