Thyroxine-Binding Globulin (TBG)
Explains why total T4 and T3 look off when the thyroid itself is working normally.
Consider this test if:
- Total T4 or T3 looks abnormal but TSH and free T4 appear normal
- On estrogen therapy, oral contraceptives, or pregnant, with confusing thyroid numbers
- Investigating discordant thyroid panels in liver disease, nephrotic syndrome, or androgen use
- A suspected inherited TBG excess or deficiency in the family
- HSA/FSA eligible
- Results delivered to your dashboard · Reviewed by a real clinician
- Drawn at a CLIA/CAP-accredited lab near you ·
Pre-test considerations
No fasting required. Note any estrogen, oral contraceptive, androgen, or thyroid medication you take, along with pregnancy status, since all shift TBG levels and are central to interpretation.
Video consult with your Care Team
A 1:1 call to discuss your health.
What members say on Trustpilot
What this test is for
Thyroxine-binding globulin (TBG) is a liver-made protein that carries most of the thyroid hormone in your blood, accounting for roughly three-quarters of plasma thyroxine-binding activity. When TBG rises or falls, total T4 and T3 shift with it, which can mimic thyroid disease on standard testing even when the gland is functioning normally. Measuring TBG separates a binding-protein issue from real thyroid dysfunction. TBG runs high with estrogen (oral contraceptives, pregnancy, hormone therapy) and hepatitis, and low with cirrhosis, nephrotic syndrome, androgen use, and inherited TBG deficiency. It is most useful as a tie-breaker, ordered when total thyroid hormone results do not fit the clinical picture or TSH and free T4 results.
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 Fast, dashboard-delivered results
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
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
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 — 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.
Recently viewed
Loading essentials…