Thyroid Hormone Tests

Submitted on March 27, 2012

The working and efficiency of the thyroid gland is checked through blood tests. The thyroid gland is responsible for creating hormones that control the way energy is used by the body. This gland is shaped like a butterfly and is in front of the trachea. This hormone is necessary for the development of the brain, specially till the child is three years old.

Thyroid Hormone Blood Tests

Some of the tests to check the thyroid hormone are as follows -

Total thyroxine

A lot of the thyroxine (T4) is attached to the thyroxine-binding globulin, which is a protein. A bit of the T4 remains unattached. The Total Thyroxine blood test measures the free and the bound thyroxine. The former is known to affect the tissue function of the body.

Free thyroxine (FTI or FT4)

The free T4 can be measured through this test. Through the FTI, the physician can understand the amount of T4 present as compared to the tyroxine-binding globulin.

Triiodothyronine (T3)

This blood test is done to measure the free and bound triiodothyronine.


Thyroid hormone testing is done for the following reasons –

Through these tests, physicians can find out the cause behind the abnormal thyroid-stimulating hormone (TSH) test.

If a person is getting treated for thyroid disease, then thyroid hormone tests are done to assess the impact of the treatment.

These tests are often done on newborn babies to check if the thyroid gland is functioning normally. Sometimes, babies have congenital hypothyroidism, which can prevent the child from growing and developing normally, and some kids might also become mentally retarded if the problem is not treated immediately.


Certain medicines might affect the results of the test. So do tell your doctor about any medicines that you are taking. If you are on thyroid medicines, then do inform your doctor about when you took the dose. If you have any concerns regarding the test, then speak to your doctor about those.


A blood test is undertaken as a part of this test. A health professional or technologist will draw a blood sample using the standard procedure. An elastic band is wrapped around your upper arm to stop the flow of blood and increase the size of your blood vessels. The area where the needle will be inserted is cleaned with alcohol, and then a sterile needle is inserted and a sample of the blood is collected for the tests.