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.
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.
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.
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.
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.
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.
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.