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The page below is a sample from the LabCE course Laboratory Assessment of Thyroid Function. Access the complete course and earn ASCLS P.A.C.E.-approved continuing education credits by subscribing online.

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Hyperthyroidism: Primary Versus Secondary

Hyperthyroidism may be referred to as "thyrotoxicosis" or toxic levels of thyroid hormone being produced. Similar to hypothyroidism, cases of hyperthyroidism may be broadly categorized as primary and secondary.

Primary hyperthyroidism relates to the thyroid gland producing large amounts of hormone due to either uncontrolled growth of hormone-producing functional tissue or by way of an autoimmune process that interferes with the normal feedback control.
  • Primary hyperthyroidism (also called “thyrotoxicosis”) is caused by:
    • Thyroid nodules
    • Thyroid adenoma
    • Graves’ disease
    • Thyroiditis
Secondary hyperthyroidism may be attributed to an over-stimulation of the thyroid. This may be due to increased production of TSH from the pituitary gland or TSH-secreting tumor, or more rarely from overproduction of TRH from the hypothalamus or thyrotropin-releasing hormone (TRH)-secreting tumor.
  • Secondary (or non-thyroidal) hyprthyroidism
    • Carcinoma
    • TSH-secreting tumors
    • TRH-secreting tumors