Ablative dose of radioiodine

  • In the context of hyperthyroidism, this indicates a dose of radioiodine that aims to render the thyroid under active. The term is also used in thyroid cancer after thryoid surgery to indicate a dose of radioiodine that aims to ablate any remaining thyroid tissue and eliminate any residual cancer.


  • This is a failure of the body to recognise particular cells as its own resulting in the malfunctioning of these cells, e.g. Addison`s disease due to adrenal anti-bodies.

Block and Replace

  • A regime of medical treatment used by some centres in patients with an over active thyroid. Anti-thyroid medication is given in higher doses to block thyroid hormone production and levothyroxine is used to replace and normalise thyroid function.

Free T3

  • This is a more active form of thyroid hormone. 20% of free T3 is secreted by the thyroid. The remainder is generated by conversion of free T4 to T3 elsewhere in the body.

Free T4

  • Free T4 is only released from the thyroid. T4, like T3 is bound proteins and it is only the free forms (free T3 and T4) that have a biological effect.


  • An enlarged thyroid gland. This can occur normally during puberty and pregnancy.


  • An over active thyroid


  • An under active thyroid

Grave`s disease

  • An autoimmune disease that is associated with the clinical features of an over active thyroid, enlarged thyroid (goitre) and thyroid eye disease. Not all these features are present in all patients. In contrast to some other causes of an over active thyroid, Graves disease not infrequently responds permanently to anti-thyroid medication.


  • Radioiodine is iodine that is radioactive. It is used in the treatment of hyperthyroidism and can be administered as a tablet or liquid. Please see the article on radioiodine for further details.


  • This is a protein produced solely by the thyroid. Its measurement is often used to detect any residual thyroid tissue in patients treated for thyroid cancer.


  • Removal of part or all of the thyroid by surgery. These are referred to a partial and total thyroidectomy respectively.

Thyroid stimulating hormone

  • A hormone that is release from the pituitary gland and stimulates the thyroid gland to produce thyroxine. Levels are typically low with an over active thyroid and raised with an under active thyroid.

Toxic multi-nodular goitre

  • An over active thyroid caused by multiple nodules in the thyroid that over produce thyroid hormone. This condition is not likely to respond permanently to anti-thyroid medication and usually requires thyroid surgery or radioiodine therapy.

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