Thyroid Panel (Total T4, T3 Uptake, Free Thyroxine Index)
Estimates free thyroid hormone by correcting for the proteins that carry it in the blood.
Consider this test if:
- Symptoms of an over- or under-active thyroid: fatigue, weight change, temperature intolerance, palpitations, or mood changes
- Pregnancy, estrogen therapy, or oral contraceptives that shift thyroid-binding proteins and distort Total T4
- Following up an abnormal thyroid result with a free-hormone estimate
- Tracking thyroid status while on thyroid hormone replacement or antithyroid medication
- HSA/FSA eligible
- Typical results in 1-2 days · Reviewed by a real clinician
- Drawn at a CLIA/CAP-accredited lab near you ·
Pre-test considerations
No fasting required. If you take thyroid medication, keep the timing of your dose consistent across tests so results are comparable, and note recent biotin supplements, which can interfere with some immunoassays.
Video consult with your Care Team
A 1:1 call to discuss your health.
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What this test is for
This panel combines three measurements to assess thyroid function: Total T4 (all the thyroxine in the blood), T3 Uptake (an indirect read on how much thyroid-binding protein is available), and the Free Thyroxine Index, a calculation that uses the first two to approximate free, biologically active T4. The index corrects for situations where binding proteins are shifted, such as pregnancy, estrogen therapy, or oral contraceptives, where Total T4 alone can mislead. High results point toward hyperthyroidism (weight loss, palpitations, heat intolerance, anxiety, tremor), while low results point toward hypothyroidism (fatigue, weight gain, cold intolerance, dry skin, brain fog).
Note that this version does not include TSH, the most sensitive first-line marker of thyroid status. If you want a starting-point thyroid screen, the related panel that adds TSH (Total T4, T3 Uptake, TSH, Free Thyroxine Index) is the more common default; this panel is useful when you specifically want the T4 and index without the pituitary signal.
Biomarkers tested
Includes 3 biomarkers
The free T4 index is a calculated estimate of active, unbound thyroxine, correcting for the binding proteins that can distort total T4 readings and give a cleaner read on how much thyroid hormone is actually available to your tissues. Doctors use it as a backup or alternative to direct free T4 when protein levels are shifting, from pregnancy, oral estrogen, liver disease, or acute illness. Low values point toward hypothyroidism, with fatigue, weight gain, cold intolerance, hair thinning, and constipation, while high values point toward hyperthyroidism, with anxiety, palpitations, heat intolerance, and unintended weight loss, and either result is best interpreted alongside TSH.
- Specimen
- Serum or plasma
- Method
- Calculated
- Measures
- Mass concentration
T3 resin uptake doesn't measure thyroid hormone directly. It measures how much binding capacity is left on thyroxine-binding globulin (TBG), the protein that carries thyroid hormone through your blood, by seeing how much added radiolabeled T3 gets picked up by a resin instead of binding to TBG. Doctors pair it with total T4 or T3 to calculate a free thyroxine index, which corrects for conditions like pregnancy, estrogen use, or liver disease that raise or lower TBG and can otherwise make thyroid results look abnormal when actual hormone activity is normal, useful when thyroid symptoms like fatigue, weight change, or temperature sensitivity don't match your TSH.
- Specimen
- Serum or plasma
- Measures
- Number fraction (%)
Total T4 measures all the thyroxine circulating in your blood, both the small free fraction that acts on cells and the larger portion bound to carrier proteins. Because binding proteins shift with pregnancy, estrogen, and liver or kidney conditions, total T4 can rise or fall without your actual thyroid function changing, which is why it's usually read alongside TSH and free T4 rather than alone. It's most useful for catching those binding-protein effects and rounding out the picture when TSH looks off but the cause isn't yet clear.
- Specimen
- Serum or plasma
- Measures
- Mass concentration
What to expect
- 1 Book instantly
Click, book, done. Choose a convenient lab location near you. Transparent, up-front pricing.
- 2 Quick lab visit
Testing to fit your busy schedule, usually 15 minutes or less. Walk-in and appointments available.
- 3 Typical results in 1-2 days
Your results post straight to your dashboard as soon as the lab completes them.
- 4 Expert guidance
Included with Mito membership. A clinician reviews your results and your personalized action plan follows, with clear next steps.
Everything your health needs,
in one membership
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Every test at our cost
Members pay our cost on every test, with lab fees passed straight through. The full receipt is itemized, never padded.
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Year-round clinician support
Text anytime and get clinician-reviewed answers. When you want to go deeper, 1:1 consultations are available at affordable rates.
All for $9/month
Order any test or consult without joining. For $9/month, members unlock member prices, trend tracking, and year-round clinician guidance.
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Frequently asked questions
View all FAQsHow does pricing work?
Every test shows the member price next to the standard non-member price, so you can see what membership saves you. The member price is our cost — covering the lab and what it takes to run the service — never a profit on the test itself; Mito makes its money on the $9 membership, not on marking up your tests. Membership is $9/mo, and you still pay the lab’s order fee. Prices are itemized before you pay, with no hidden fees.
Where do I get tested?
Choose a partner lab (Quest, Labcorp, or BioReference) at checkout. If your cart spans multiple tests, we consolidate the whole order onto a single lab so you only make one visit.
Is this eligible for HSA/FSA?
Yes. This test is HSA/FSA eligible, and you can pay with your HSA/FSA card at checkout.
When will I get my results?
Your results post to your dashboard once your lab completes them, then a clinician reviews them and your full analysis and personalized action plan (with clear next steps) follow. Turnaround varies by test: specialty assays and at-home kits take longer, and each test shows its expected turnaround before you buy.
Do I need a doctor’s order?
No. Mito provides the lab order for you, so you can book and get tested without a separate doctor visit.
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