Empeiria

Thyrotropin

Also known as TSH, thyroid stimulating hormone, thyrotropin

protein · no single molecular formula

LOINC 3016-3 code verified serum mIU/L

unverified These explanations are written to be easy to read and have not yet been checked against a source. The ranges and measurement notes on this page show theirs.

definition unverified

Not a thyroid hormone itself. It is the instruction your brain sends to your thyroid telling it how hard to work.

Anterior pituitary glycoprotein hormone driving thyroid follicular output, under negative feedback from circulating free thyroid hormone.

function unverified

Your brain watches thyroid hormone levels and adjusts this signal to keep them steady, the way a thermostat adjusts a heater.

Your brain watches thyroid hormone levels and adjusts this signal to keep them steady, the way a thermostat adjusts a heater.

No clinical version written yet.

why measured unverified

Because it is a signal rather than the hormone, it shifts before the hormones do. That makes it the most sensitive early test.

Because it is a signal rather than the hormone, it shifts before the hormones do. That makes it the most sensitive early test.

No clinical version written yet.

if high unverified

Counter-intuitively, a high result usually means an UNDERactive thyroid. Your brain is shouting because the gland is not responding. Think of it as the volume of the instruction, not the amount of hormone.

Counter-intuitively, a high result usually means an UNDERactive thyroid. Your brain is shouting because the gland is not responding. Think of it as the volume of the instruction, not the amount of hormone.

No clinical version written yet.

if low unverified

Usually an overactive thyroid. Your brain has gone quiet because there is already plenty of hormone in circulation.

Usually an overactive thyroid. Your brain has gone quiet because there is already plenty of hormone in circulation.

No clinical version written yet.

caveats unverified

Levels move in a daily rhythm and are higher at night. A short illness can push it around temporarily, so an odd result during sickness is usually repeated once you are well.

Levels move in a daily rhythm and are higher at night. A short illness can push it around temporarily, so an odd result during sickness is usually repeated once you are well.

No clinical version written yet.

What this substance is

A glycoprotein hormone whose sugar chains vary between molecules, so there is no single exact structure even in principle. Assays target the protein portion.

UniProt P01222

3D model · Protein (predicted)

Predicted structure of TSH's beta chain only (AlphaFold). Working TSH is an alpha/beta pair; the alpha chain is shared with LH, FSH and hCG. Predicted by AlphaFold (model v6, average confidence 86 of 100); its sequence matches UniProt exactly. Colour is AlphaFold's own confidence for each part: dark blue very high (above 90), light blue confident (70-90), yellow low (50-70), orange very low (below 50). Drag to rotate, scroll to zoom.

Reference ranges

Checking your own result against this range needs the running application; this is a static copy. Nothing you type anywhere in Empeiria is ever sent to a server.

This open edition shows a range only where a public-domain or openly licensed source states one, and none does for this marker yet. Compare your result with the range printed on your own lab report.

How it is measured

In practice

A health worker takes a small amount of blood from a vein in your arm with a needle. You usually do not need to fast. If you take biotin (vitamin B7), talk to your provider before the test, because it can affect the result. Some other medicines can too, so tell your provider what you take.

Venous blood sample, often drawn with free/total T4, T3 and anti-TPO. No preparation is needed for TSH itself, though fasting may apply if other tests are ordered on the same draw. Drugs that may need to be stopped briefly include amiodarone, dopamine, lithium, potassium iodide and glucocorticoids. Biotin (B7) can affect TSH results; patients taking biotin should discuss it with their provider before thyroid function testing.

Before the test

If you take biotin, talk to your provider before the test.
Tell your provider about every medicine you take; do not stop any unless told to.

Where: laboratory

Sources: TSH (Thyroid-Stimulating Hormone) Test, MedlinePlus (U.S. National Library of Medicine); TSH test, MedlinePlus Medical Encyclopedia cited · not yet checked by a person

In the lab

immunoassay

Third-generation chemiluminescent sandwich immunoassay

Antibodies catch the hormone and a light-emitting tag reports how much was caught. Modern versions can measure very low levels, which matters because a suppressed result is as meaningful as a raised one.

Two-site (sandwich) antibody capture with a chemiluminescent read-out.

What can throw it off

Biotin supplements
Heterophile antibodies
Macro-TSH

Why labs disagree: Assays are calibrated to WHO international reference preparations made from pituitary TSH, which differs from the TSH circulating in blood, and they are not yet harmonised. Results can differ by up to 50% between platforms, so a change of laboratory can look like a change in thyroid status when nothing has changed.

Sources: Laboratory Procedure Manual, Thyroid Stimulating Hormone (Beckman Access hTSH), NHANES 2011-2012, CDC/NCHS; Thyroid Stimulating Hormone and Thyroid Hormones (Triiodothyronine and Thyroxine): An American Thyroid Association-Commissioned Review of Current Clinical and Laboratory Status. Thyroid 2023 (PMC open access) cited · not yet checked by a person

What it reports on

pituitary gland secreted by
TSH is a hormone made by the pituitary gland.
thyroid gland regulated by
Thyroid hormone levels set how much TSH the pituitary makes, so TSH is the first test used to check the thyroid.

Associated symptoms

When high

high Feeling tired all the time · non specific · common
high Feeling cold when others do not · suggestive · common
Thyroid hormone sets basal metabolic rate and therefore heat production.
high Gaining weight without eating more · suggestive · common
high Difficulty passing stool · non specific · occasional
high Dry, rough skin · suggestive · common
high Hair thinning or falling out · suggestive · occasional
high Feeling low or flat · non specific · occasional
high Trouble thinking clearly · non specific · common

When low

low Overheating easily · suggestive · common
low Noticing your heartbeat · suggestive · common
Excess thyroid hormone increases heart rate and contractility.
low Losing weight without trying · suggestive · common

Conditions this marker features in

When high

high Mildly underactive thyroid · defining
ETA 2013 definition: TSH above the reference range with normal thyroid hormones; mild 4.0-10.0 mU/L, more severe above 10 mU/L. A raised result is repeated after 2-3 months, and TSH is checked at least yearly once treatment starts.
high Underactive thyroid · defining
TSH above the reference range is part of the definition, and is usually the first test checked.

When low

low Overactive thyroid · defining
Suppressed (low) in hyperthyroidism, and usually the first test checked. It can be undetectable even in mild cases.

Either direction

either Low white blood cell count · supportive
Autoimmune thyroid disease was a common cause found in one study of isolated leukopenia. TSH was part of the workup.

Ordered as part of