TSH (thyroid-stimulating hormone) test: what it means
What it measures
The TSH test is a blood test that measures thyroid-stimulating hormone (also called thyrotropin), a hormone made by the pituitary gland. TSH tells the thyroid how much thyroid hormone to make, so the TSH level reflects how the pituitary and thyroid are working together.
Why it’s ordered
A TSH test is used to find out how well the thyroid is working. It can help show whether someone has hyperthyroidism (too much thyroid hormone) or hypothyroidism (too little thyroid hormone). On its own the result does not explain the cause, so a provider interprets it alongside symptoms and other tests.
General reference range
As a general reference, MedlinePlus lists normal TSH values ranging from about 0.4 to 4.8 microunits per milliliter (µU/mL). Important caveat: these are general values, not a personal cutoff. Normal ranges may vary slightly among different labs, and some labs use different measurements or test different samples; some labs also use a higher upper limit for older people (as high as about 7 µU/mL). Ranges can differ by age, sex, and testing method. Because of this, a single number should never be read as a diagnosis on its own — the range printed on your own lab report is what applies to your result, and your provider interprets what your specific numbers mean.
If it’s high
A higher-than-normal TSH level is most often associated with an underactive thyroid gland (hypothyroidism). MedlinePlus notes there can be many causes, such as Hashimoto disease (a form of thyroiditis). This is a general possible association, not a diagnosis and not a complete list; the pituitary may make more TSH when thyroid hormone in the blood is low, as a signal for the thyroid to work harder.
If it’s low
A lower-than-normal TSH level may be associated with an overactive thyroid gland (hyperthyroidism). Conditions that can be seen with this include Graves disease, toxic nodular goiter or multinodular goiter, too much iodine in the body (for example from iodine contrast used during imaging tests), or taking too much thyroid hormone medicine or supplements that contain thyroid hormone. Certain medicines may also be linked to a lower-than-normal TSH, including glucocorticoids/steroids, dopamine, some chemotherapy medicines, and opioid painkillers such as morphine. These are general possible associations, hedged and not exhaustive, and not a diagnosis. Your results are interpreted by a healthcare provider in the context of your symptoms, history, other test results, and any medicines you take. This is general information, not medical advice.
A result is not a diagnosis
Reference ranges vary by laboratory, age, sex, and method — the range on your own report is what applies to you. A single value out of range doesn’t confirm any condition; your clinician interprets it alongside your symptoms, history, and other results. This page is general information, not medical advice.
Medicines that can move this result
It is thyroid hormone itself, so the pituitary senses plenty in the blood and stops sending TSH. Dosing is titrated against TSH for exactly this reason, and a dose that is slightly too high pushes TSH below normal even when you feel fine.
Source ↗Lithium concentrates in the thyroid and blocks the release of thyroid hormone, so the gland underproduces and the pituitary answers by pushing TSH up. The label describes goiter and hypothyroidism with lowered T3 and T4, which is the picture that comes with a high TSH.
Source ↗Each tablet carries a large iodine load, which can either shut the thyroid down (TSH rises) or drive excess hormone release (TSH falls), so the direction depends on which reaction you have. The label puts hypothyroidism at up to 10% of patients and hyperthyroidism at about 2%.
Source ↗It is prescribed to slow an overactive thyroid, and a dose that is slightly too strong tips the gland into underproduction, which drives TSH up. That is why the label asks for routine TSH and free T4 checks with dose adjustment.
Source ↗The drug releases the brakes on the immune system to attack cancer, and the same immune cells can inflame the thyroid. The label reports hypothyroidism in 8% of patients (a high TSH) and hyperthyroidism in 3.4% (a low TSH), and an overactive phase can precede lasting underactivity, so either direction is possible.
Source ↗High-dose biotin, common in hair, skin and nail supplements, interferes with the assay chemistry rather than with your thyroid, so the printed TSH can be wrong while the gland is normal. The levothyroxine label tells patients to stop biotin and biotin-containing supplements for at least 2 days before thyroid testing.
Source ↗Only relevant if you take levothyroxine. Proton pump inhibitors such as omeprazole reduce stomach acid, and stomach acid is needed to absorb the thyroid tablet, so less gets in and TSH can drift up on a dose that used to work.
Source ↗Do not stop a prescribed medicine over a lab number. These are recognised associations, not a finding about your result — your value may have nothing to do with any medicine you take, and the list is not complete. Bring it to whoever prescribed the drug; they can weigh it against why you are taking it.
Frequently asked
- What does the TSH (thyroid-stimulating hormone) test measure?
- The TSH test is a blood test that measures thyroid-stimulating hormone (also called thyrotropin), a hormone made by the pituitary gland. TSH tells the thyroid how much thyroid hormone to make, so the TSH level reflects how the pituitary and thyroid are working together.
- What is a normal TSH (thyroid-stimulating hormone) test range?
- As a general reference, MedlinePlus lists normal TSH values ranging from about 0.4 to 4.8 microunits per milliliter (µU/mL). Important caveat: these are general values, not a personal cutoff. Normal ranges may vary slightly among different labs, and some labs use different measurements or test different samples; some labs also use a higher upper limit for older people (as high as about 7 µU/mL). Ranges can differ by age, sex, and testing method. Because of this, a single number should never be read as a diagnosis on its own — the range printed on your own lab report is what applies to your result, and your provider interprets what your specific numbers mean.
- What does a high result mean?
- A higher-than-normal TSH level is most often associated with an underactive thyroid gland (hypothyroidism). MedlinePlus notes there can be many causes, such as Hashimoto disease (a form of thyroiditis). This is a general possible association, not a diagnosis and not a complete list; the pituitary may make more TSH when thyroid hormone in the blood is low, as a signal for the thyroid to work harder.
- What does a low result mean?
- A lower-than-normal TSH level may be associated with an overactive thyroid gland (hyperthyroidism). Conditions that can be seen with this include Graves disease, toxic nodular goiter or multinodular goiter, too much iodine in the body (for example from iodine contrast used during imaging tests), or taking too much thyroid hormone medicine or supplements that contain thyroid hormone. Certain medicines may also be linked to a lower-than-normal TSH, including glucocorticoids/steroids, dopamine, some chemotherapy medicines, and opioid painkillers such as morphine. These are general possible associations, hedged and not exhaustive, and not a diagnosis. Your results are interpreted by a healthcare provider in the context of your symptoms, history, other test results, and any medicines you take. This is general information, not medical advice.
Other lab tests
Sources
General reference, not medical advice, and not a substitute for your clinician. Lab reference ranges and interpretation depend on the laboratory and on your individual situation — discuss your results with a licensed healthcare professional.