T3 Uptake (T3RU)
An older way to estimate free thyroid hormone, pairing binding-protein availability with total T4 and TSH.
Consider this test if:
- Fatigue, weight change, temperature intolerance, palpitations, or hair thinning that points toward thyroid dysfunction
- Confirming or monitoring suspected hypothyroidism or hyperthyroidism
- Total T4 looks off and binding-protein changes from pregnancy, estrogen, or other medications may be the cause
- Wanting TSH alongside an estimated free thyroxine index in one panel
- HSA/FSA eligible
- Typical results in 1 day · Reviewed by a real clinician
- Drawn at a CLIA/CAP-accredited lab near you ·
Pre-test considerations
No fasting required. Biotin supplements can interfere with immunoassay-based thyroid results, so pause high-dose biotin for about 48 hours before the draw. Note any thyroid medication, estrogen, or recent contrast exposure, since these affect thyroid hormone levels and binding proteins.
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What this test is for
T3 uptake is an indirect measure of available thyroid-binding sites on proteins like thyroxine-binding globulin (TBG), despite its name it does not measure serum T3. On its own it means little; combined with total T4 it is used to calculate the free thyroxine index (FTI), an estimate of how much T4 is biologically available. This panel reports T3 uptake, total T4, TSH, and the calculated FTI, which together help evaluate suspected hyperthyroidism or hypothyroidism and the symptoms that prompt thyroid testing: fatigue, weight change, temperature intolerance, palpitations, hair thinning, and mood or sleep disturbance.
This is an older approach to estimating free hormone; most current workups start with TSH and use a direct free T4 assay, and this panel does not detect T3 thyrotoxicosis, which requires free T3. It remains useful when binding-protein changes (pregnancy, estrogen, certain medications) distort total T4 and you want the FTI to correct for them.
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 day
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.
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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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Upload past labs and watch your trends over time. Every marker and visit lives in one longitudinal record, so all your care stays together.
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Text anytime and get clinician-reviewed answers. When you want to go deeper, 1:1 consultations are available at affordable rates.
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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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