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Hyperthyroidism is the condition that occurs from an overactive thyroid. Primary hyperthyroidism occurs because of a problem within the thyroid gland itself and secondary hyperthyroidism is a result of stimulation of the thyroid gland from excess TSH (thyroid stimulating hormone) in circulation[1].

Hyperthyroidism can be caused due to the autoimmune disease Grave's disease, a condition caused by the immune system attacking the thyroid organ, causing over-production of thyroid hormone[2][3].

When stimulated by TSH the thyroid gland produces Thyroxine and Triiodothyronine, T4 and T3 respectively. T4 is produced in larger amounts but is inactive and must be converted to active T3. The release of T4 and T3 stimulates the negative feedback loop of the release of TSH from the anterior pituitary gland. Levels of TSH will be reduced and T4 will be increased in people with hyperthyroidism in comparison to the reference ranges which may change between laboratories[4].


  1. http://patient.info/doctor/hyperthyroidism
  2. https://www.niddk.nih.gov/health-information/endocrine-diseases/hyperthyroidism
  3. https://www.niddk.nih.gov/health-information/endocrine-diseases/graves-disease
  4. http://www.pathology.leedsth.nhs.uk/pathology/ClinicalInfo/CommonTestsInvestigations/ThyroidFunctionTests/tabid/113/Default.aspx
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