Free T3 Levels Test
Free T3 Levels Test can be requested without a referral, and this overview covers what to expect. A free T3 test measures the amount of triiodothyronine (T3) in your blood that is not attached to proteins. It is ordered to help evaluate thyroid function, especially when total T3 or other thyroid tests give unclear results.
- Sample type
- blood
- Category
- Thyroid
- Turnaround
- 1-3 business days
- Price
- $198
- Referral
- Not required
A free T3 test measures the amount of triiodothyronine (T3) in your blood that is not attached to proteins. It is ordered to help evaluate thyroid function, especially when total T3 or other thyroid tests give unclear results.
What it measures
- Free T3 — The active, unbound form of T3 hormone that can enter cells and affect metabolism.
- Total T3 (sometimes) — Measures both bound and free T3; may be included for comparison.
- Free T4 (sometimes) — Another thyroid hormone, often checked alongside free T3.
- TSH (sometimes) — A pituitary hormone that signals the thyroid; helps interpret T3 levels.
Who it is for
A healthcare provider typically orders this test when symptoms suggest an overactive thyroid (hyperthyroidism) or when other thyroid tests are inconclusive. It may also be used to monitor treatment for thyroid conditions.
Preparation
No fasting is usually required. Tell your provider about any medications or supplements you take, as some can affect T3 levels.
Results and what they mean
Results are reported as a number with a reference range, which varies by lab. A clinician interprets your free T3 level along with your symptoms and other tests. This is general information, not medical advice; discuss your results with a qualified healthcare professional.
How to order this test
- Choose the test and place a confidential order online.
- Select a certified collection site and pick a time that suits you.
- Have your specimen collected — most draws take only a few minutes.
- Review results in a secure portal, typically within 1–3 days.
Preparation, hours, and pricing vary by site; confirm details directly with the lab before your visit.
Availability by state
Direct-access online ordering for the free t3 levels test is available in most states. It is currently unavailable in 6 states:
Everywhere else you can order confidentially and collect your sample at a certified site. Browse by state →
Frequently asked questions
Do I need to fast for a free T3 test?
No, fasting is not typically required. You can eat and drink normally unless your provider gives other instructions.
What can affect my free T3 level?
Medications (like thyroid pills or steroids), pregnancy, severe illness, and some supplements can affect results. Always share your medication list with your provider.
How soon will I get my results?
Most labs return free T3 results within 1 to 3 business days. Your provider’s office will contact you about the next steps.
Is this test the same as a total T3 test?
No. Free T3 measures only the unbound, active hormone, while total T3 measures both bound and free T3. They give different information.