Thyroid function test (TSH)

Alternative Names: TSH

Thyroid function tests measure the amount of thyroid stimulating hormone (TSH) in the blood in order to diagnose or exclude an over-active thyroid gland (thyrotoxicosis) or under-active thyroid gland (hypothyroidism). A sample of blood is withdrawn through a needle inserted in a vein, usually in the area inside the elbow, and sent for laboratory analysis.

What is it?
A toxicology screen is a test to detect the presence of legal and illegal drugs. It may be performed on blood or urine.

The sample can be obtained at your doctor’s rooms, a clinic, or in hospital. The analysis is performed in a laboratory.

Why is it done?
TSH is done to diagnose or exclude:

• An over-active thyroid gland (thyrotoxicosis)
• An under-active thyroid gland (hpothyroidism)

TSH is a hormone, secreted by the pituitary (small gland in the brain), which stimulates the thyroid gland to secrete thyroid hormones (T3 and T4). There is a “feedback loop” whereby low levels of thyroid hormone stimulate more TSH release, and high levels of thyroid hormone suppress TSH release. It is for this reason that TSH is a useful measurement in thyroid disease – low levels imply thyrotoxicosis and high levels imply hypothyroidism. In primary pituitary gland disease, TSH levels will always be low, because it is the pituitary gland that produces TSH.

What happens?

Before – how to prepare
No special preparation is necessary.

During – how the test is done
A convenient area, where there are prominent veins, is identified and cleaned – the area inside the elbow is often used. A tourniquet or tight band is applied above the area in order to increase pressure and dilate the veins. A needle is then inserted, through the skin, into a vein, and some blood is withdrawn. The needle may cause some pain but this is not usually severe. The blood specimen is sent to the laboratory for analysis.

After the test
You will have a small dressing over the puncture wound, which can be removed after a few hours.

Risks and Compilations
There is a slight risk of excessive bleeding at the puncture site and an even smaller risk of infection.

Short Description
Thyroid function tests measure the amount of thyroid stimulating hormone (TSH) in the blood in order to diagnose or exclude an over-active thyroid gland (thyrotoxicosis) or under-active thyroid gland (hypothyroidism).

Keywords
thyroid function test, TSH, thyrotoxicosis, hypothyroidism