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TSH (thyrotropin)
The pituitary hormone that tells the thyroid how hard to work — the first-line test of thyroid function.
Other names: Thyroid-stimulating hormone, thyrotropinSection: Thyroid
Updated: August 29, 2026·MedProtect editorial team Reference information — not a diagnosis or a prescription
In shortThe usual adult reference range is 0.4–4.8 mIU/L. Some laboratories set the upper limit for older people as high as 7 mIU/L, and pregnancy has its own trimester-specific ranges.
Reference ranges
Group
Reference range
Adults
0.4–4.8 mIU/L
Older adults, at some laboratories
Upper limit up to 7 mIU/L
During treatment for a thyroid disorder
Usually kept between 0.4 and 4.8 mIU/L
Pregnancy
A different, trimester-specific range applies
Normal value ranges vary slightly among different laboratories, and experts do not fully agree on where the upper limit should be when diagnosing thyroid disorders. The same units may appear on reports as µU/mL or µIU/mL — all three notations describe equal measures.
Reference range vs optimal — not the same thing
The formal reference often extends to ~4.0 mIU/L. When hypothyroid symptoms are present, many endocrinologists target 0.5–2.5 mIU/L: values of 2.5–4.0 may warrant monitoring in sensitive patients, and the upper limit is much lower in pregnancy. Treatment decisions belong with your doctor.
Check your value
Enter the number from your lab report — see how it compares with the typical range. Mind the units shown in the chosen row.
A rough comparison with a typical range, not a diagnosis. Reference ranges vary between laboratories — check the range on your own report and let a clinician interpret the result.
What this marker is
TSH stands for thyroid-stimulating hormone. It is produced by the pituitary gland and prompts the thyroid gland to make and release thyroid hormones into the blood. Because the pituitary reacts sensitively to any change in thyroid output, TSH is the test most often ordered first when an overactive or underactive thyroid is suspected, and it is the standard test for monitoring treatment of these conditions. A TSH check may also be suggested when a pregnancy is being planned.
The result is read through a feedback loop. When the thyroid underproduces, the pituitary releases more TSH to stimulate it, so a higher-than-normal TSH most often means an underactive thyroid. When the thyroid overproduces, the pituitary pulls TSH down. That is why TSH is usually interpreted together with the hormones themselves — free T4 and free T3 — and sometimes with anti-TPO antibodies, which show whether an autoimmune process is involved.
Results are reported in milli-international units per liter (mIU/L). The same quantity appears on some reports as microunits per milliliter — µU/mL or µIU/mL; these are equal measures, not different tests. TSH values vary during the day, so an early-morning blood draw is considered the best option.
No special preparation is needed for the test. Several medicines can affect the result — amiodarone, dopamine, lithium, potassium iodide, prednisone and other glucocorticoids — and the provider may ask to pause some of them for a short time. The vitamin biotin (B7) can also distort TSH results, so the provider needs to know about it before any thyroid function test. No medicine should be stopped without the provider's advice.
When it is high
Underactive thyroid (hypothyroidism)A higher-than-normal TSH is most often due to an underactive thyroid gland — the pituitary releases more hormone to stimulate a sluggish thyroid.
Hashimoto diseaseAutoimmune thyroiditis is the classic cause of hypothyroidism: the immune system damages the thyroid, hormone output falls, and TSH rises.
Individual treatment targetsDuring treatment for a thyroid disorder the level is usually kept within 0.4–4.8 mIU/L, but exceptions exist — with a pituitary cause of the thyroid problem, during pregnancy, or after certain thyroid cancers, the target range is different.
When it is low
Overactive thyroid (hyperthyroidism)A lower-than-normal TSH may be due to an overactive thyroid gland — the pituitary reduces TSH because the blood already carries too much thyroid hormone.
Graves disease and toxic goiterGraves disease, toxic nodular goiter, and multinodular goiter are the typical causes of an overactive thyroid.
Excess iodine or thyroid hormoneToo much iodine in the body — for example from iodine contrast used in imaging tests such as a CT scan — or taking too much thyroid hormone medicine, including over-the-counter supplements that contain thyroid hormone, can suppress TSH.
Certain medicinesGlucocorticoids and steroids, dopamine, certain chemotherapy medicines, and opioid painkillers such as morphine can lower TSH.
Expected in some situationsWhen a pituitary disorder is the cause of the thyroid problem, a low TSH may be expected; with a history of certain types of thyroid cancer, a below-normal TSH may be the goal, to reduce the chance of the cancer coming back.
What can skew the result
These factors can shift the value without any disease — worth considering before a retest:
Time of day — values vary, an early-morning draw is preferredBiotin (vitamin B7) supplementsAmiodarone, dopamine, lithium, potassium iodide, prednisone and other glucocorticoidsPregnancy — a trimester-specific range appliesAge — some laboratories raise the upper limit for older people
How to prepare
No special preparation is needed. The provider should know about all medicines and supplements, especially biotin; some medicines may be paused for a short time, but nothing is stopped without the provider's advice. An early-morning blood draw is preferred because TSH varies during the day.
When a retest makes sense
An abnormal TSH is usually read together with free T4 and free T3 before any conclusion. During treatment for a thyroid disorder, TSH is the main monitoring test: the level is typically kept between 0.4 and 4.8 mIU/L, except when a pituitary disorder is the cause, when there is a history of certain thyroid cancers, or during pregnancy.
Who usually reviews this result
A result outside the reference range is usually reviewed by: an endocrinologist; your GP or primary care doctor for the first evaluation. Bring your lab report and any previous results to the appointment.
Names used on lab reports
Your report may use any of these names: TSHThyrotropinThyroid stimulating hormoneThyrotropin test
Units
Measured in: mIU/L
Several markers on your report?
See how MedProtect explains results in the app: the whole report, a check of the recognized values, and a clear breakdown.
Yes. TSH values vary during the day, and an early-morning sample is considered the best option. For monitoring, repeating the test at roughly the same time of day makes results easier to compare.
Which medicines and supplements interfere?
Amiodarone, dopamine, lithium, potassium iodide, prednisone and other glucocorticoids can affect the result, and so can biotin (vitamin B7). The provider decides whether any of them should be paused — nothing should be stopped without that advice.
Is the same range used during treatment?
Usually the target is 0.4–4.8 mIU/L, but there are exceptions: a pituitary cause of the thyroid problem, a history of certain thyroid cancers, and pregnancy each change the target. The treating provider sets the individual goal.
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