What Factors Affect Thyroxine Levels?

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  • Written By: B. Chisholm
  • Edited By: O. Wallace
  • Last Modified Date: 12 September 2019
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Thyroxine levels may be influenced by many factors, both internal and external. Autoimmune diseases, tumors, a deficiency of iodine and some medications may cause either an increase or decrease in thyroxine levels. Specific symptoms are experienced if the thyroxine levels are not right. Treatment is achieved either by treating the cause or thyroxine replacement or anti-thyroid drugs, depending on whether the thyroxine levels are lowered or raised.

The thyroid gland, which is situated in the neck, is where thyroxine, and other thyroid hormones are produced, in response to a complex feedback mechanism in the body. The correct functioning of the thyroid gland, and release of the various thyroid hormones, including thyroxine, is necessary for the body to function optimally. The thyroid hormones are essential for metabolism and maintaining the balance of calcium in the body.

A number of autoimmune diseases can affect thyroid levels. An autoimmune disease refers to a state in which the body's antibodies attack their own tissues, in this case the thyroid tissues. Grave's Disease occurs when antibodies stimulate the production of thyroxine, raising the levels and causing hyperthyroidism. In the case of autoimmune thyroiditis, the antibodies cause the thyroid to produce less thyroxine, resulting in hypothyroidism, or low thyroxine levels.


A deficiency of iodine, not often seen in the developed world but more prevalent in developing countries, results in lower thyroxine levels, as the thyroid gland needs iodine to function. Congenital hypothyroidism is also sometimes seen when a baby is born with an underactive thyroid gland. Pituitary gland dysfunction may also lower levels.

Some drugs such as lithium, which is usually used for bipolar disorder, and amiodarone, a cardiac drug, may affect thyroxine levels. Levels may be raised by a number of other conditions. These include ovarian teratomas or tumors, cancer or goiter, where the thyroid gland is enlarged significantly.

The symptoms of both hyperthyroidism and hypothyroidism are generally quite specific, allowing for diagnosis, backed up by measurement of the thyroid hormone levels. High thyroxine levels, usually presents with weight loss, irritability and anxiety, amongst other symptoms. Conversely, low thyroxine levels may cause weight gain, tiredness and feeling cold.

Correction of thyroid levels entails removing any causative factors, such as medications. Pharmacological treatment of high thyroxine consists of using anti-thyroid drugs, such as carbimazole, radiotherapy or, in some cases, surgery. For low levels of thyroxine, synthetic levothyroxine is used as replacement therapy. Depending on the cause of the change in thyroxine levels, treatment may need to be lifelong.


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