TSH with Reflex to Free T4
The most sensitive first-line marker for thyroid function, behind fatigue, weight change, and mood shifts.
Consider this test if:
- Fatigue, unexplained weight change, cold or heat intolerance, or low mood
- Hair thinning, dry skin, constipation, or a racing heart with tremor and anxiety
- A family history of thyroid disease or autoimmune conditions
- Establishing a thyroid baseline or screening as part of a general checkup
- On thyroid medication and confirming the dose has your level in range
- HSA/FSA eligible
- Typical results in 1-2 days · Reviewed by a real clinician
- Drawn at a CLIA/CAP-accredited lab near you ·
Reflex testing
If your TSH comes back outside the standard range, a free T4 test runs automatically to help distinguish subclinical from overt thyroid dysfunction and guide next steps. This is done at no additional cost.
Pre-test considerations
No fasting required. TSH follows a daily rhythm, running higher in the early morning and lower in the afternoon, so for tracking over time draw at a consistent time of day. Biotin supplements can distort immunoassay results, so pause high-dose biotin for about 48 hours beforehand. Note any thyroid medication and its timing, since recent doses affect interpretation.
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What this test is for
TSH (thyroid-stimulating hormone) is the pituitary signal that tells your thyroid how much thyroid hormone to make, and it is the standard first test for screening thyroid function. A high TSH points toward an underactive thyroid (hypothyroidism), commonly linked to fatigue, weight gain, cold intolerance, dry skin, constipation, and low mood, while a low TSH points toward an overactive thyroid (hyperthyroidism), linked to weight loss, racing heart, anxiety, tremor, and heat intolerance. Because the pituitary responds sharply to small changes in thyroid hormone, TSH shifts before free T4 does, which is why it is the sensitive screening marker when pituitary disease is not suspected. A normal TSH excludes most primary thyroid disease.
This is the routine status test. The separate Thyroid Panel (Total T4, T3 uptake, TSH, free thyroxine index) and Thyroiditis Panel (which adds thyroid antibodies) are used when you already suspect specific thyroid disease or want to characterize its cause.
Biomarkers tested
Includes 1 biomarker
TSH is the pituitary's signal to the thyroid, rising when it senses too little thyroid hormone in circulation and falling when there's too much. High TSH points to an underactive thyroid, often behind fatigue, weight gain, cold intolerance, constipation, dry skin, and low mood. Low TSH points to an overactive thyroid, showing up as anxiety, racing heart, weight loss, heat intolerance, or sleep trouble, and it's the single most sensitive marker for catching thyroid dysfunction before it fully unravels your energy, weight, and cycle.
- Specimen
- Serum or plasma
- Measures
- Concentration
Free T4 measures the unbound thyroxine circulating in blood, the active thyroid hormone available for cells to pull in and convert into T3, which drives your metabolic rate, body temperature, and energy production. Low free T4 points to an underactive thyroid and pairs with fatigue, weight gain, cold intolerance, constipation, and brain fog, while high free T4 suggests hyperthyroidism and tracks with anxiety, racing heart, weight loss, and heat intolerance. Run it alongside TSH to see whether the pituitary and thyroid are communicating properly, which clarifies whether a TSH abnormality reflects true thyroid dysfunction or something upstream.
- Specimen
- Serum or plasma
- Measures
- Mass concentration
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 1-2 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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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.
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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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