Thyroid Stimulating Hormone, commonly called TSH, is a simple blood test that helps assess the function of the pituitary and thyroid gland. In this article, we shall take a brief look at TSH and its clinical implications.
TSH
TSH is released by the pituitary gland. Once released, it travels through the blood stream and reached the thyroid gland. It stimulates the thyroid gland to release two main hormones – T4 and T3, both of which have numerous functions in the body.
Performing a TSH assessment
A TSH blood test is a simple blood test. Prior to the blood test, any drugs that are being taken that can affect the function of the thyroid gland need to be stopped if possible. These drugs include lithium, amiodarone and prednisolone (steroids). The test is straightforward and involves obtaining a blood sample from a small vein in the arm. This can be slightly painful and feels like a sharp ‘sting’, which is to be expected and is short-lived.
Once the blood sample is obtained, it is sent to the biochemistry lab for analysis.
Clinical Implications
The TSH test indicates whether the thyroid gland is overactive and underactive. Patients who have these conditions can experience a variety of symptoms which can have a significant impact on various vital systems such as the heart and the digestive system.
Normal and Abnormal Values
Normal values of TSH range between 0.4 – 4 mIU/L. Levels below this mean that there is too much T4 and T3 that is exerting a ‘negative effect’ onto the pituitary. This is called hyperthyroidism, commonly called an overactive thyroid. Hyerthyroidism is seen in conditions such as Graves disease and toxic goitre.
The opposite i.e. high levels of TSH mean that the thyroid is underactive – also called hypothyroidism.
There are certain drugs that can affect TSH levels that can ultimately affect the functioning of the thyroid gland. These include amiodarone and lithium, as previously mentioned.
Problems
Sometimes, TSH levels can be abnormal when a patient has an infection or illness. These are non-specific changes, and the tests are repeated after a few weeks to months following conclusion of treatment to obtain true values.
Sometimes, the value of TSH may be normal but will be associated with high or low levels of thyroid hormones T4 and T3. This is called a ‘subclinical’ picture, and either warrants observation or treatment based on the cause and patients symptoms.
Conclusion
TSH is a useful test to determine the function of the pituitary gland and its effect on thyroid function.