What is TSH?
TSH is produced by the pituitary gland and tells the thyroid gland how much thyroid hormone to make. It is the most sensitive and widely used test for thyroid function.
TSH is measured on a logarithmic scale, meaning a TSH of 0.5 vs. 1.0 is a much bigger change than 3.0 vs. 3.5. Lab reference ranges can vary; some experts advocate for narrower ranges (0.5–2.5 mIU/L) for optimal health.
Why might TSH be high?
A high TSH suggests the pituitary is working harder than usual to stimulate the thyroid, which often means the thyroid is underactive (hypothyroidism). The TSH response amplifies small changes in thyroid hormone — small TSH changes can be significant.
This information is educational. A single out-of-range result is rarely the whole picture — a healthcare professional can interpret your numbers alongside your overall health and history.
Context questions that matter
- →Was this result slightly or clearly outside the reference range?
- →Were related markers also high or low?
- →Is this new compared with previous tests?
- →Could recent illness, exercise, fasting, alcohol, supplements, or medication affect it?
- →Do you have symptoms that should be discussed with a clinician?
Markers often reviewed together with TSH
Clinicians rarely look at one number in isolation. These markers usually accompany TSH on a thyroid panel and help put the result in context.
Lifestyle considerations
- •TSH values can fluctuate slightly throughout the day; testing at the same time of day improves consistency
Questions to ask your doctor
- →How does this result fit with TSH, Free T4, Free T3 and thyroid antibodies?
- →Could timing, medication, supplements such as biotin, or recent illness affect this result?
- →Should this be repeated, or interpreted with my symptoms and previous thyroid results?
Don't guess from one flagged result.
Start with the most relevant panel and see how your markers fit together in plain English.
Frequently asked questions
What does high TSH mean?
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A high TSH suggests the pituitary is working harder than usual to stimulate the thyroid, which often means the thyroid is underactive (hypothyroidism). The TSH response amplifies small changes in thyroid hormone — small TSH changes can be significant.
What is TSH?
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TSH is produced by the pituitary gland and tells the thyroid gland how much thyroid hormone to make. It is the most sensitive and widely used test for thyroid function.
Should TSH be read with Free T4 and Free T3?
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Thyroid markers are usually interpreted together. TSH, Free T4, Free T3 and sometimes thyroid antibodies (TPO, Tg) provide more context than any single result, particularly when TSH is borderline.
Can supplements or timing affect thyroid results?
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Time of draw, thyroid medication timing, acute illness, pregnancy and supplements such as biotin can affect some thyroid assays. If a repeat test is suggested, ask your doctor how to prepare so the two values are comparable.
What supports healthy TSH levels?
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TSH values can fluctuate slightly throughout the day; testing at the same time of day improves consistency