Triiodothyronine (T3), Total
Confirms an overactive thyroid when TSH and T4 look normal or borderline.
Consider this test if:
- Symptoms of an overactive thyroid (weight loss, palpitations, tremor, heat intolerance) with a normal or borderline T4
- Working up unexplained fatigue and weight loss, or proximal muscle weakness
- Following a known thyroid nodule or Graves' disease over time
- Confirming T3 thyrotoxicosis suspected from a low TSH
- 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 distort immunoassay thyroid results, so stop high-dose biotin for about 48 hours before the draw. If you take thyroid hormone, note the dose and timing, since it raises measured T3.
Video consult with your Care Team
A 1:1 call to discuss your health.
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What this test is for
Total triiodothyronine (T3) measures both the protein-bound and free forms of T3, the more biologically active thyroid hormone. It is most useful for catching hyperthyroidism that standard testing can miss, particularly T3 thyrotoxicosis, where T3 rises while T4 stays within range. Elevated T3 appears in Graves' disease, toxic nodules, and multinodular thyrotoxicosis, and the test is often added when there are clear signs of an overactive thyroid (unexplained weight loss, palpitations or supraventricular tachycardia, tremor, heat intolerance) but a normal T4. Because most T3 in the blood is bound to carrier proteins, this result shifts with conditions that change those proteins, such as pregnancy or estrogen use.
This is the total T3 measurement. The separate Free T3 test isolates the unbound, active fraction, and reverse T3 measures an inactive form used for specific questions about T3 metabolism.
- Specimen
- Serum or plasma
- Measures
- Mass concentration
What you'll learn
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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.
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Your personalized action plan. Nutrition, supplements, and training in one clinician-reviewed protocol, updated as your results change.
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Track your trends. Upload results from any lab and see each biomarker trend over time, so you know what is working.
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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
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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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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.
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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.
Mito Membership
$9 /mo
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Without membership
$0
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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. 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.
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