Thyroid health
Thyroid-stimulating hormone (TSH)
Thyrotropin
Included in every MyHealthspan membership: Focus, Baseline, and Complete.
Compare membershipsUsually the first test of how your thyroid is working.
TSH is made by the pituitary gland at the base of your brain and tells your thyroid how much hormone to make. Because it responds to small shifts in thyroid hormone, it's usually the first test used to check thyroid function.
TSH moves in the opposite direction to thyroid hormone.
When thyroid hormone levels fall, the pituitary sends out more TSH to push the thyroid harder. When levels rise, TSH drops. So a higher TSH often points to an underactive thyroid, and a lower TSH often points to an overactive one.
TSH can change before free T4 and free T3 move outside their reference ranges. It can't show what's causing a thyroid problem, so it's read with free T4, free T3, your symptoms, and your history.
When thyroid hormone runs low, TSH rises to compensate.
Questions
What can affect my TSH result?
Serious illness can lower TSH for a short time, levels are often a little lower early in pregnancy, and TSH can run higher in older adults. Some medicines matter too. Biotin supplements can interfere with some thyroid tests, so mention it if you take biotin.
What happens if my TSH is out of range?
A licensed nurse practitioner reviews your result alongside your free T4 and free T3. A single TSH outside the range is often rechecked, since illness and other short-term factors can shift it. A change that persists is worth following up with a clinician.