Thyroid Stimulating Hormone (TSH)
TSH stimulates the thyroid gland (found in the front of the neck) to release the hormones thyroxine and triiodothyronine.
When the pituitary gland is damaged, it does not release enough TSH to stimulate the Thyroid gland to release thyroxine and triiodothyronine.
Thyroxine is converted into triiodothyronine and most of this occurs in the cells of the body.
Thyroxine and triiodothyronine are essential for metabolism, digestive function, heart function, development of the brain, muscle control and bone maintenance.
Further reading at You & Your Hormones here.
Testing for TSH deficiency
Blood test: Your TSH levels and free thyroxine can be measured in a routine blood test, usually carried out in your hospital phlebotomy department, your GP practice or in a community blood test unit.
Some thyroid function tests only measure TSH routinely.
If there is secondary thyroid insufficiency (from hypopituitarism) then measuring TSH alone will not necessarily help.
Free thyroxine (T4) must be measured alongside the TSH.
This is sometimes supported by a free triiodothyronine test (T3). This test can be difficult to interpret because the conversion of thyroxine (T4) into triiodythyronine (T3) occurs mostly in the cells of the body.
Hormone replacement for TSH deficiency
You will usually be given a Thyroxine replacement medication, rather than TSH.
In the UK and Europe this is often called Levothyroxine.
This is then monitored through routine blood tests.
Symptoms of TSH deficiency may include dry skin, constipation, reduced tolerance to cold, weight gain and hair loss.