TSH, or thyroid-stimulating hormone, is a pituitary hormone that prompts the thyroid gland to produce its hormones. It is ordered to assess the thyroid axis, often with free T4 and free T3. It does not confirm or rule out a condition on its own, and the range printed on your report is the one that applies.
TSH is a signal rather than a hormone that acts directly on most tissues. The thyroid's own output is measured by free T4 and free T3, and the three results are usually read as one picture. A TSH value on its own can mislead, because the pituitary adjusts its output to compensate for a thyroid gland that is producing more or less hormone than the loop expects.
What the test measures
TSH is a glycoprotein hormone made by the anterior pituitary. It travels to the thyroid gland and binds receptors on thyroid cells, prompting them to take up iodine and produce thyroxine (T4) and triiodothyronine (T3). It also supports the gland's growth and structure.
The loop is closed by feedback. T4 and T3 circulating in the blood signal back to the pituitary and the hypothalamus, and the pituitary adjusts its TSH output in response. When thyroid hormone is low, TSH usually rises; when thyroid hormone is high, TSH usually falls. That relationship is why TSH is read with free T4 rather than on its own.
Why it may be ordered
- As part of a thyroid profile or a general health checkup.
- When symptoms or history raise a question about thyroid function, so the clinician can see the pituitary side of the loop.
- To follow a known thyroid condition over time, alongside free T4.
- During pregnancy, when thyroid physiology changes and the usual picture shifts.
It is not a universal screening test, and a result inside the printed range is not proof that nothing is wrong. The test is one line in an assessment that includes the thyroid hormone results, antibodies where relevant, and the person's history.
The unit on your report
| What you may see | What it means |
|---|---|
| TSH, thyrotropin, thyroid-stimulating hormone | The test name. Laboratories abbreviate it differently. |
| mIU/L | Milli-international units per litre, the unit most reports use. |
| uIU/mL | The same quantity expressed per millilitre. It is the same scale as mIU/L. |
| mU/L | Another way some laboratories print the same unit. |
| Assay or method name | Some reports name the method. Sensitivity differs between assays, which is one reason ranges differ. |
Why this page does not print a range
A reference range is built from a reference population, using a particular method on a particular analyser. TSH ranges differ between laboratories for that reason, and they can also shift with age, sex, and the context the sample was taken in. A number copied from a website is not your range, even when the unit matches.
The range printed on the report that produced your value is the one that applies. Doctano keeps that printed range with the result and does not replace it with a general range.
What a high value can mean
A higher TSH means the pituitary is signalling the thyroid more strongly. It can be associated with a thyroid gland that is producing less hormone than the loop expects, because the pituitary raises its output to compensate. Possible contributors include autoimmune thyroid disease, earlier thyroid surgery or other thyroid procedures, and some medicines.
A high TSH can also occur while free T4 still sits inside its printed range, and it can occur during recovery from a severe illness or with an assay that is affected by antibodies in the sample. None of those possibilities is settled by the TSH value alone; a clinician reads the pattern with free T4, the history, and the trend.
What a low value can mean
A lower TSH means less pituitary drive. It can be associated with a thyroid gland producing more hormone than the loop expects, or with thyroid hormone taken as a medicine. Less often it reflects a problem at the pituitary or hypothalamic level, where TSH and free T4 can both be low.
Severe illness, some medicines, and pregnancy can also lower TSH without a thyroid disorder being present. A low TSH is therefore not interpreted in isolation, and it is not automatically a better result than a high one.
What can move the value
- Time of day. TSH has a daily rhythm and is released in pulses, so the hour of the draw can matter.
- Recent illness. Recovery from a severe illness can suppress TSH for a period.
- Pregnancy. Thyroid physiology and hormone requirements change during pregnancy.
- Medicines. Thyroid hormone, some steroids, and some medicines that act on dopamine signalling can change TSH. A clinician can say whether a medicine is relevant.
- Assay interference. Antibodies in the sample can affect some TSH assays and not others.
- Method and calibration. Different laboratories can produce small differences on the same sample.
What to compare it with
Read TSH with free T4 first, then free T3 where it is printed. Free T4 shows what the thyroid gland is producing, and TSH shows how the pituitary is responding to it. TPO antibodies add a different piece of information, about an autoimmune contribution, and they do not replace the hormone results.
The most useful comparison is the previous TSH from the same laboratory, because method and range stay consistent. When the laboratory changes, a small difference may reflect the assay rather than a real change.
How to see the trend
Doctano reads the TSH value, its unit, and the reference range printed on the report. It keeps the range with the result, normalizes the marker name across laboratories, and places the value on the profile's timeline. Each point still opens the report it came from, so the original page can be checked.
If two reports use different units or different assay names, Doctano normalizes the unit for the timeline. Verify the value and the unit against the original report before treating a change as real, especially when the two results came from different laboratories.
What this page is not
This page explains the test in general. It does not interpret your result, diagnose a condition, or recommend treatment. It is not medical advice. Verify the value and the unit against the original report, and discuss the result with a qualified professional.