TSH (thyroid-stimulating hormone)

What is TSH?

TSH is produced by the pituitary gland. It tells the thyroid to create thyroid hormones and release them into the blood.

  • The thyroid is a gland beneath the larynx (voice box) at the front of the throat.
  • The pituitary gland is in the base of the skull, beneath the brain and behind the bridge of the nose.

TSH ensures that the body maintains constant levels of the thyroid hormones thyroxine (T4) and triiodothyronine (T3) in the blood, which help control the rate at which the body uses energy.

Hormones from the thyroid pass directly out into the blood and affect our metabolism. Most people's thyroid glands function well, however around 5% of the population suffer from various thyroid disorders. These disorders are due to an over- or underproduction of thyroid hormones.

TSH tests can be ordered at regular intervals, especially when being treated for thyroid disorders. If a patient's dose of thyroid medicine has been adjusted, it is recommended to wait 6 to 8 weeks before testing the TSH level again. Testing before that time makes it impossible to establish the effect of the medicine on the thyroid.

Why do we analyse TSH?

TSH tests measure the amount of thyroid-stimulating hormone (TSH) in the blood.

There are several reasons why TSH levels should be analysed. The main reason is to find out whether the thyroid is functioning the way it should. If the thyroid is failing to work properly, this means that you have either an underactive thyroid (hypothyroidism) or an overactive thyroid (hyperthyroidism).

Suffering from an underactive thyroid (hypothyroidism) often causes symptoms such as:

  • Weight gain
  • Fatigue
  • Constipation
  • Feeling cold
  • Frequent periods

People suffering from an overactive thyroid (hyperthyroidism) experience more or less the opposite symptoms:

  • Weight loss
  • Rapid pulse
  • Diarrhoea
  • Feeling hot
  • Irregular periods

If you are suffering from any of these symptoms, a TSH test can determine why. For example, your thyroid may be damaged or you may have problems with the pituitary gland or hypothalamus.

It is also a good idea to find out your TSH levels to see whether your hypothyroidism or hyperthyroidism treatment – involving thyroid medication, surgery or radiotherapy – is working.

High levels of TSH

High levels are seen in cases of primary hypothyroidism (underactive thyroid).

Low levels of TSH

Low levels are seen in cases of hyperthyroidism (overactive thyroid) and pituitary failure.


Browse Our Tests


Go to Thyroid Disorder Info.

Take a look at Reviews to find out what our users think of us.