Markers · Thyroid
A TSH in range, and you're still tired. TSH, read against the rest of you.
What TSH measures, what it does in the body, why it's tested, and the two ranges it's read against. Everything said about the marker here comes from Merlin's own biomarker catalogue.
What TSH is
TSH is a pituitary hormone that regulates thyroid gland activity and the production of thyroid hormones T3 and T4. Elevated TSH suggests the pituitary is working harder to stimulate an underactive thyroid (hypothyroidism), while low TSH indicates the thyroid may be overactive (hyperthyroidism) or the pituitary is being suppressed. TSH is considered the most sensitive and first-line marker for assessing overall thyroid function and feedback loop integrity.
What it does in the body
TSH is secreted by the anterior pituitary gland in response to thyrotropin-releasing hormone (TRH) from the hypothalamus. It binds to receptors on the thyroid gland to stimulate synthesis and release of triiodothyronine (T3) and thyroxine (T4), which regulate metabolism, thermogenesis, heart rate, growth, and neurological development through a classic negative feedback loop.
Why it's tested
TSH is used to screen for, diagnose, and monitor thyroid disorders including hypothyroidism, hyperthyroidism, subclinical thyroid dysfunction, and to guide thyroid hormone replacement therapy. It is also used in evaluating infertility, fatigue, weight changes, mood disorders, and cardiovascular risk.
The two ranges
The reference range reflects population statistics. The target reflects physiology.
- Lab reference range
- 0.45-4.5 mIU/L
- Functional target
- 1.0-3.0 mIU/L
Those are different numbers, and you deserve to know which one you're looking at. Merlin reads your result against both.
Where this lives
A Field Guide to Thyroid & Adrenal Health
The field guide that covers TSH in depth, whole and public.
In a real read
The real read on this site is a Cardiovascular one, so there's no TSH in it. What it shows is the shape: one system, thought all the way through, with the score, the narrative and the layers underneath. Every system you have data for gets one of these, and a thyroid panel is read the same way, against everything else you brought.
A real Cardiovascular surface from a real anonymized panel: the score, the narrative, the layers underneath. Yours will be built the same way, on your own numbers.
Educational context for your conversations with your licensed healthcare provider, not a diagnosis or a treatment plan. Merlin reads results; it doesn't diagnose.
Bring the panel this number came from. Merlin reads it against everything else you have, every system and every year, then shows you what it means and what's worth finding out next. Start with your first month.
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