Surgery or radioactive treatment to the thyroid gland

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These are common causes of hypothyroidism in the UK due to increasing use of these treatments for other thyroid conditions.

Other causes

Other causes of hypothyroidism are less common and include:

A side-effect to some medicines. For example, amiodarone and lithium.
Other types of 'thyroiditis' (thyroid inflammation) caused by infection or other rare conditions.
A pituitary gland problem is a rare cause. The pituitary gland that lies just under the brain makes a hormone called thyroid stimulating hormone (TSH). This stimulates the thyroid gland to make thyroxine. If the pituitary does not make TSH, then the thyroid cannot make enough thyroxine.
Some children are born with an underactive thyroid gland (congenital hypothyroidism).

How is hypothyroidism diagnosed?

A blood test can diagnose hypothyroidism. 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. It is released into the bloodstream. It stimulates the thyroid gland to make thyroxine. If the level of thyroxine in the blood is low, then the pituitary releases more TSH to try and stimulate the thyroid gland to make more thyroxine. Therefore, a raised level of TSH means the thyroid gland is underactive and is not making enough thyroxine.
Thyroxine (T4).

A low level of T4 confirms hypothyroidism.

Note: some people have a raised TSH but have a normal T4. This means that you are making enough thyroxine but the thyroid gland is needing extra 'stimulation' from TSH to make the required amount of thyroxine. In this situation you have an increased risk of developing hypothyroidism in the future. Your doctor may advise a repeat blood test every so often to see if you do eventually develop hypothyroidism.Other tests are not usually necessary unless a rare cause of hypothyroidism is suspected. For example, tests of the pituitary gland may be done if both the TSH and T4 are low.