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.
Video consult with your Care Team
A 1:1 call to discuss your health.
What members say on Trustpilot
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.
- Specimen
- Serum or plasma
- Measures
- Number fraction (%)
What you'll learn
-
Insights that connect the dots. A clinician reads your whole picture, not one result in isolation, connecting family history, past results, and lifestyle into clear next steps.
-
Your personalized action plan. Nutrition, supplements, and training in one clinician-reviewed protocol, updated as your results change.
-
Track your trends. Upload results from any lab and see each biomarker trend over time, so you know what is working.
-
Never miss a recheck. Mito tells you what is worth retesting and when, then reminds you so nothing slips.
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.
Everything your health needs,
in one membership
-
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.
-
Continuous tracking, all in one place
Upload past labs and watch your trends over time. Every marker and visit lives in one longitudinal record, so all your care stays together.
-
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.
Mito Membership
$9 /mo
cancel anytime
Without membership
$0
pay as you go
At-cost pricing on labs, scans, and more
Supplements at 30% off retail prices Coming soon
On-demand clinician consults when you need guidance
Personalized action plans across supplements, exercise, nutrition, and sleep
AI health coaching to help you act on your results
Year-round medical support, with in-chat clinician escalation
All your health records in one personal vault, with trends and biological age tracking
Early access to new diagnostics and product releases
More tests to consider
Loading essentials…
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. It is never a profit on the test itself. Mito makes its money on the $9 membership, not on marking up your tests. Membership is $9 per month, and any applicable lab order or draw fee is itemized before you pay.
Where do I get tested?
Choose an available partner lab at checkout. If your cart contains multiple blood tests, Mito helps consolidate the eligible tests at one lab when possible. At-home kits and scans follow the collection or appointment process shown on their product page.
Is this eligible for HSA/FSA?
Yes. Eligible tests can be paid for with an HSA or FSA card at checkout.
When will I get my results?
Your results appear in your Mito dashboard after the laboratory completes processing. A clinician then reviews them before your analysis and personalized action plan are finalized. Timing varies by test, and specialty assays and at-home kits may take longer.
Do I need a physician's order?
No. Mito provides the laboratory order when one is required, so you do not need to arrange a separate physician visit before purchasing.
Recently viewed
Loading essentials…