Home › Lab markers › TSH (Thyroid Stimulating Hormone)
METABOLIC & HORMONE MARKERS
Also printed as: TSH · Thyrotropin
Educational only — not medical advice.
TSH is the signal your pituitary gland sends to tell your thyroid how hard to work. It moves in the opposite direction to thyroid hormone: when thyroid output is low, TSH rises to push harder. That inversion is the single most confusing thing about this test.
TSH is the standard first-line thyroid test because it is sensitive to small changes. But it is a signal about thyroid output, not a measure of it, so free T4 is often needed to complete the picture.
TYPICAL ADULT RANGE
Many labs report roughly 0.4–4.5 mIU/L for adults. Ranges vary by lab, by pregnancy status, and somewhat with age. Reported in mIU/L.
Reference ranges vary by lab, by method, and by age and sex. Always read your own result against the range printed on your report.
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A low TSH means the pituitary is easing off, which usually happens when thyroid hormone is on the higher side. Common contributors include thyroid hormone medication dosed a little high, recent illness, pregnancy in the first trimester (which naturally lowers it), and high-dose biotin supplements, which interfere with the assay itself and are a genuinely common cause of odd thyroid results. Stopping biotin for a few days before a redraw is a standard step your doctor may suggest. Persistent low values with symptoms are worth discussing promptly.
A high TSH means the pituitary is pushing harder, which usually points toward lower thyroid output. Very often the explanation is mild and stable — subclinical patterns are common, particularly with age, and many are simply monitored. Recent illness, poor sleep, time of day (TSH is higher in the early morning), and biotin supplements can all shift the value. A single mildly high TSH is commonly repeated with a free T4 before any conclusion is drawn, and whether anything should change is your doctor's call with you.
Your doctor is the one who can read this number against your history, symptoms, and medications.
Educational only — not medical advice. Lab results only mean something alongside your history, symptoms, medications, and the rest of your panel. Bring questions to your doctor; they are the one who can interpret your results for you.
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