Thyroid-Stimulating Immunoglobulin (TSI)
The antibody that drives Graves' disease and confirms autoimmune hyperthyroidism.
Consider this test if:
- Lab results already show hyperthyroidism (low TSH, high free T4) and you need to confirm Graves' disease
- Symptoms of overactive thyroid: weight loss, palpitations, tremor, heat intolerance, anxiety, or eye changes
- Pregnant or planning pregnancy with a history of Graves' disease, to gauge risk to the baby
- Deciding between antithyroid drugs, radioiodine, or surgery, since high levels predict drug resistance
- Tracking whether antibody levels are falling during treatment or before stopping medication
- HSA/FSA eligible
- Typical results in 2-4 days · Reviewed by a real clinician
- Drawn at a CLIA/CAP-accredited lab near you ·
Pre-test considerations
No fasting required and no specific time of day is needed. A standard blood draw is all that is involved.
Video consult with your Care Team
A 1:1 call to discuss your health.
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What this test is for
Thyroid-stimulating immunoglobulins are IgG autoantibodies that bind and activate the TSH receptor, pushing the thyroid to overproduce hormone. This test measures those stimulating antibodies and is the most specific way to confirm Graves' disease as the cause of hyperthyroidism, which shows up as weight loss, racing heart, tremor, heat intolerance, anxiety, insomnia, and eye changes. It is most useful once TSH and free T4 already point to an overactive thyroid and you need to know whether autoimmunity is behind it. Markedly elevated TSI also predicts a poorer response to antithyroid drugs and a higher chance of relapse, which informs whether medication, radioiodine, or surgery is the better path. In pregnancy it matters because these antibodies cross the placenta and can cause neonatal hyperthyroidism, so a high maternal level flags the newborn for monitoring.
TSI measures the antibody that actively stimulates the thyroid, which is distinct from TPO antibodies (a marker of autoimmune thyroiditis such as Hashimoto's) and from TSH itself (which measures thyroid function, not its cause).
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 2-4 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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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
pay as you go
At-cost pricing on labs, scans, and more
Priority turnaround on your results
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
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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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