How is hyperthyroidism diagnosed?
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A blood test can diagnose hyperthyroidism. A normal blood test will also rule it out if symptoms suggest that it may be a possible diagnosis. One or both of the following may be measured:
- Thyroid-stimulating hormone (TSH). This hormone is made in the pituitary gland in the brain. It is released into the bloodstream. It stimulates the thyroid gland to make thyroxine. If the level of thyroxine in the blood is high, then the pituitary releases less TSH. Therefore, a low level of TSH means the thyroid gland is overactive and is making too much thyroxine.
- Thyroxine (T4). A high level of T4 confirms hyperthyroidism.
Other tests are sometimes done to clarify the cause. For example, an ultrasound scan of the thyroid or a thyroid scan may be done if you have a nodular goitre. Other blood tests may be done if a rare cause is suspected.
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