Last Review Date: April 1, 2017
The thyroid is a small, butterfly-shaped gland just below the Adam's apple. This gland plays a very important role in controlling your body's , that is, how your body functions. It does this by producing thyroid hormones (thyroxine, or T4, and triiodothyronine, or T3), chemicals that travel through your blood to every part of your body. Thyroid affect almost all tissues in the body and regulate many aspects of metabolism.
If you have enough thyroid hormone in your blood there is a and the gland stops making the hormones. When the body needs more thyroid hormones, the gland starts producing again.
The pituitary gland, located at the base of the brain, tells the thyroid when to start and stop. The pituitary sends thyroid-stimulating hormone (TSH) to the thyroid and this hormone increases the production of thyroid hormones by the thyroid gland.
Talking Results: what your Thyroid Function Test results can show
Hyperthyroidism means you have too much thyroid hormone. This causes a range of problems for the body and these are described in our article on Graves' disease. As well as Graves’ disease hyperthyroidism can be caused by a thyroid adenoma – a small benign tumour in the thyroid gland that produces excessive thyroid hormones and by taking excessive amounts of thyroid hormone therapy. Treatment for hyperthyroidism involves having a single dose of radioactive iodine by mouth or by injection, taking anti-thyroid tablets regularly, or surgery. Many times all three methods are appropriate, while at other times a single treatment may be the best option.
Hypothyroidism means you have too little thyroid hormone. This causes many tissues to function abnormally. See our article on Hashimoto's disease. Hypothyroidism is common and the onset can be very slow so that you can have hypothyroidism for a number of years before it is recognised and treated. Hypothyroidism can also develop after treatment of hyperthyroidism, especially after surgery or radioactive iodine treatment. Congenital hypothyroidism is rare but important to detect and treat immediately. It is one of the conditions looked for in newborn screening programs in Australia. It may be due to a poorly developed thyroid gland or a normal-sized gland that does not produce enough thyroid hormones. Treatment for all types of hypothyroidism is usually straightforward and involves taking tablets of thyroid hormone regularly.
Thyroid cancer is fairly uncommon. Most people who have thyroid cancer have excellent chances of surviving for a long time. For instance, in younger patients, with the most common forms of thyroid cancer there is a better than 95 per cent cure rate if the cancer is treated appropriately. There are five main types of thyroid cancer: papillary, follicular, medullary, anaplastic and thyroid lymphoma. Papillary and follicular cancers are the most common and are slow growing and usually straightforward to treat. Treatment may be monitored by measurement of the thyroid protein thyroglobulin in blood. Medullary thyroid cancer usually has a good outcome if it has not spread beyond the thyroid gland; it may produce excessive amounts of the hormone calcitonin, which can be used to monitor treatment. Anaplastic thyroid cancer is the least common but it is the most aggressive form and spreads quickly. It can be difficult to treat. Lymphoma, a tumour composed of (the cells that produce immunity from bacteria and viruses), can also occur in the thyroid.
Solitary thyroid nodule
A solitary thyroid nodule is a small lump on the thyroid gland. As many as 50 per cent of the population will have a nodule somewhere in the thyroid, however, the overwhelming majority of these nodules are harmless. Occasionally, thyroid nodules can be cancerous and need to be treated.
Thyroiditis is of the thyroid gland. It may be associated with either hypo- or hyperthyroidism. It may be painful, feeling like a sore throat, or painless. Thyroiditis may be due to an autoimmune disorder (especially Hashimoto’s thyroiditis), an infection, exposure to a chemical that is toxic to the thyroid, or due to an unknown cause (). Depending on the cause, it can be but transient or .
A thyroid goitre is a dramatic enlargement of the thyroid gland. This rarely happens in developed countries because iodine supplementation of some foods is common and this prevents severe iodine deficiency. Goitres are often removed for cosmetic reasons or because they compress other vital structures of the neck, including the windpipe (trachea) and the tube that leads from your mouth to your stomach, the oesophagus.
The first test your doctor will usually order to detect a problem with your thyroid gland is a TSH test. If your TSH level is abnormal, the doctor will usually request a free thyroxine (FT4 ) test to confirm the diagnosis. A free triiodothyronine (FT3) test may be requested as well.
Additional tests that may be performed include:
- Thyroid antibodies - to identify autoimmune thyroid conditions.
- Thyroid peroxidase (TPO) antibody - a marker for autoimmune thyroid disease; it can be detected in Hashimoto’s thyroiditis or Graves’ disease. It may be especially helpful in early Hashimoto’s thyroiditis when TSH is elevated but the remaining thyroid maintains a normal free T4 level.
- Thyroid stimulating hormone receptor (TSHR) antibodies - a marker for Graves’ disease.
- Thyroglobulin - to monitor the treatment of thyroid cancer and to detect recurrence.
When are these tests ordered?
Because one out of every 4,000 infants is born without a working thyroid gland, there is a national programme in Australia to screen all newborn babies for hypothyroidism with a TSH test on a drop of blood taken from a heel prick.
Otherwise, these tests are requested when your doctor notices that your symptoms resemble those of a thyroid condition. For instance, signs of hypothyroidism include fatigue, weight gain, increased sensitivity to cold, and skin dryness. Signs of hyperthyroidism include fatigue, weight loss, increased sensitivity to heat, and nervousness. Tests are also requested in individuals who have a family history of thyroid disorders.
Talking Results: what your Thyroid Function Test results can show
1. Are any thyroid diseases hereditary?
Yes, Hashimoto’s thyroiditis and Graves’ disease may run in families.
2. Are thyroid diseases more common in men or women?
Yes, hypothyroidism is 10 times more common in women.
3. How often is pregnancy complicated by a thyroid problem?
Thyroid problems complicate 5% to 9% of all pregnancies.
On this site
Tests: TSH, free thyroxine (FT4), free triiodothyronine (FT3), thyroglobulin
Conditions: Hashimoto's thyroiditis, Graves' disease
Elsewhere on the web
Better Health Channel: Thyroid gland
healthdirect Australia: Thyroid problems
Australian Thyroid Foundation
British Thyroid Foundation - Your Thyroid Gland