The TSH test is often the first test for evaluating thyroid function and/or symptoms of hyper- or hypothyroidism. It is frequently measured together with thyroxine (usually Free T4). Other thyroid tests that may be requested include T3 (usually as Free T3) and thyroid antibodies (if autoimmune-related thyroid disease is suspected).
TSH testing is used to:
screen newborns for an underactive thyroid
diagnose a thyroid disorder in a person with symptoms
Your doctor requests this test if you show symptoms of a thyroid disorder. For example, symptoms of hyperthyroidism include heat intolerance, weight loss, rapid heartbeat, nervousness, insomnia, and breathlessness. Common symptoms of hypothyroidism include fatigue, weakness, weight gain, slow heart rate, and cold intolerance.
The test may also be requested to monitor the effectiveness of treatment when a patient is being treated for a known thyroid disorder.
The blood test may be requested with other thyroid hormone tests and after a physical examination of your thyroid. TSH screening is routinely performed in newborns. There are currently no recommendations for routine screening of adults in the UK.
A high TSH result often means an underactive thyroid gland caused by failure of the gland (hypothyroidism). Very rarely, a high TSH result can indicate a problem with the pituitary gland, such as a tumour, producing uncontrolled concentrations of TSH. A high TSH value can also occur in people with underactive thyroid glands who have been receiving too little thyroid hormone medication.
A low TSH result can indicate an overactive thyroid gland (hyperthyroidism) or damage to the pituitary gland that prevents it from producing TSH. A low TSH result can also occur in people with an underactive thyroid gland who are receiving too much thyroid hormone medication.
Whether high or low, an abnormal TSH indicates an excess or deficiency in the amount of thyroid hormone available to the body, but it does not indicate the reason why. An abnormal TSH test result is usually followed by additional testing to investigate the cause of the increase or decrease.
This article was last reviewed on 19 October 2015. | This article was last modified on 30 January 2017.
The review date indicates when the article was last reviewed from beginning to end to ensure that it reflects the most current science. A review may not require any modifications to the article, so the two dates may not always agree.
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