Patients & Visitors

Endocrine Surgery

Thyroid function test

A thyroid function test may be carried out to determine whether you have an overactive or underactive gland.

Thyroid function test measures the amount of certain types of hormones in your blood. An excessive amount of the two hormones that are produced by the thyroid gland, thyroxine (T4) and triiodothyronine (T3), would indicate an underlying condition that is making your thyroid gland overactive.

If your thyroid gland is underactive, another gland, known as the pituitary gland, will produce an excess of a hormone called thyroid stimulating hormone (TSH). TSH is released by your body in order to stimulate your thyroid gland. Therefore, a high level of TSH in your blood would indicate that your thyroid gland is underactive.

A single blood sample is taken to test for both thyroid hormones and TSH.

Further blood testing for thyroid antibodies may be required if your thyroid gland is found to be either over or underactive.

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