TRH stimulation test

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TRH stimulation test
Purposeassessing the degree of suppression in suspected hyperthyroidism or hypothyroidism

Prior to the availability of sensitive TSH assays, thyrotropin releasing hormone or TRH stimulation tests were relied upon for confirming and assessing the degree of suppression in suspected hyperthyroidism. Typically, this stimulation test involves determining basal TSH levels and levels 15 to 30 minutes after an intravenous bolus of TRH. Normally, TSH would rise into the concentration range measurable with less sensitive TSH assays. Third generation TSH assays do not have this limitation and thus TRH stimulation is generally not required when third generation TSH assays are used to assess degree of suppression.


Differential diagnosis use

TRH-stimulation testing however continues to be useful for the differential diagnosis of secondary (pituitary disorder) and tertiary (hypothalamic disorder) hypothyroidism. Patients with these conditions appear to have physiologically inactive TSH in their circulation that is recognized by TSH assays to a degree such that they may yield misleading, "euthyroid" TSH results. Use and Interpretation:[ citation needed ]

• Helpful in diagnosis in patients with confusing TFTs. In primary hyperthyroidism TSH are low and TRH administration induces little or no change in TSH levels

• In hypothyroidism due to end organ failure, administration of TRH produces a prompt increase in TSH

• In hypothyroidism due to pituitary disease (secondary hypothyroidism) administration of TRH does not produce an increase in TSH

• In hypothyroidism due to hypothalamic disease (tertiary hypothyroidism), administration of TRH produces a delayed (60–120 minutes, rather than 15–30 minutes) increase in TSH

Process and interpretation

The TRH test involves administration of a small amount of TRH intravenously, [1] following which levels of TSH will be measured at several subsequent time points using samples of blood taken from a peripheral vein.[ citation needed ]

The test is used in the differential diagnosis of secondary and tertiary hypothyroidism. First, blood is drawn and a baseline TSH level is measured. Then, TRH is administered via a vein. After 30 minutes blood is drawn again and the levels of TSH are measured and compared to the baseline. Some authors recommend additional blood sampling at 15 minutes. In children, late blood sampling at 60 to 120 minutes is necessary. An increase in the serum TSH level following TRH administration means that the cause of the hypothyroidism is in the hypothalamus (tertiary hypothyroidism), i.e. the hypothalamus is not producing TRH. Therefore, when TRH is given exogenously, TSH levels increase. If the increase in serum TSH level following TRH administration is absent or very slight, then the cause of the hypothyroidism is in the anterior pituitary gland, i.e. the pituitary is not secreting TSH. Therefore, even when TRH is given exogenously, TSH levels do not rise as the pituitary is diseased.[ citation needed ]

Side effects and risks

TRH may cause nausea, vomiting and some patients experience an urge to urinate.[ citation needed ]

Rarely, TRH may cause blood vessel constriction leading to hemorrhage in patients with pre-existing pituitary tumors. Accordingly, patients should be advised about the risks, albeit rare, of TRH testing. [2]

See also

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Thyroid Endocrine gland in the neck; secretes hormones that influence metabolism

The thyroid, or thyroid gland, is an endocrine gland in vertebrates. In humans it is in the neck and consists of two connected lobes. The lower two thirds of the lobes are connected by a thin band of tissue called the thyroid isthmus. The thyroid is located at the front of the neck, below the Adam's apple. Microscopically, the functional unit of the thyroid gland is the spherical thyroid follicle, lined with follicular cells (thyrocytes), and occasional parafollicular cells that surround a lumen containing colloid. The thyroid gland secretes three hormones: the two thyroid hormones – triiodothyronine (T3) and thyroxine (T4) – and a peptide hormone, calcitonin. The thyroid hormones influence the metabolic rate and protein synthesis, and in children, growth and development. Calcitonin plays a role in calcium homeostasis. Secretion of the two thyroid hormones is regulated by thyroid-stimulating hormone (TSH), which is secreted from the anterior pituitary gland. TSH is regulated by thyrotropin-releasing hormone (TRH), which is produced by the hypothalamus.

Hypothyroidism Endocrine disease

Hypothyroidism is a disorder of the endocrine system in which the thyroid gland does not produce enough thyroid hormone. It can cause a number of symptoms, such as poor ability to tolerate cold, a feeling of tiredness, constipation, slow heart rate, depression, and weight gain. Occasionally there may be swelling of the front part of the neck due to goiter. Untreated cases of hypothyroidism during pregnancy can lead to delays in growth and intellectual development in the baby or congenital iodine deficiency syndrome.

Thyrotropin-releasing hormone Hormone

Thyrotropin-releasing hormone (TRH) is a hypophysiotropic hormone produced by neurons in the hypothalamus that stimulates the release of thyroid-stimulating hormone (TSH) and prolactin from the anterior pituitary.

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Endocrine gland Glands of the endocrine system that secrete hormones to blood

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Neuroendocrine cells are cells that receive neuronal input and, as a consequence of this input, release message molecules (hormones) into the blood. In this way they bring about an integration between the nervous system and the endocrine system, a process known as neuroendocrine integration. An example of a neuroendocrine cell is a cell of the adrenal medulla, which releases adrenaline to the blood. The adrenal medullary cells are controlled by the sympathetic division of the autonomic nervous system. These cells are modified postganglionic neurons. Autonomic nerve fibers lead directly to them from the central nervous system. The adrenal medullary hormones are kept in vesicles much in the same way neurotransmitters are kept in neuronal vesicles. Hormonal effects can last up to ten times longer than those of neurotransmitters. Sympathetic nerve fiber impulses stimulate the release of adrenal medullary hormones. In this way the sympathetic division of the autonomic nervous system and the medullary secretions function together.

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Pituitary disease Medical condition

A pituitary disease is a disorder primarily affecting the pituitary gland.

Hypothalamic–pituitary hormones are hormones that are produced by the hypothalamus and pituitary gland. Although the organs in which they are produced are relatively small, the effects of these hormones cascade throughout the body. They can be classified as a hypothalamic–pituitary axis of which the adrenal (HPA), gonadal (HPG), thyroid (HPT), somatotropic (HPS), and prolactin (HPP) axes are branches.

Hypothalamic disease is a disorder presenting primarily in the hypothalamus, which may be caused by damage resulting from malnutrition, including anorexia and bulimia eating disorders, genetic disorders, radiation, surgery, head trauma, lesion, tumour or other physical injury to the hypothalamus. The hypothalamus is the control center for several endocrine functions. Endocrine systems controlled by the hypothalamus are regulated by antidiuretic hormone (ADH), corticotropin-releasing hormone, gonadotropin-releasing hormone, growth hormone-releasing hormone, oxytocin, all of which are secreted by the hypothalamus. Damage to the hypothalamus may impact any of these hormones and the related endocrine systems. Many of these hypothalamic hormones act on the pituitary gland. Hypothalamic disease therefore affects the functioning of the pituitary and the target organs controlled by the pituitary, including the adrenal glands, ovaries and testes, and the thyroid gland.


  1. Moncayo H, Dapunt O, Moncayo R (2007). "Diagnostic accuracy of basal TSH determinations based on the intravenous TRH stimulation test: an evaluation of 2570 tests and comparison with the literature". BMC Endocr Disord. 7: 5. doi:10.1186/1472-6823-7-5. PMC   1950865 . PMID   17678551.
  2. " TRH Test". 2005-05-31. Retrieved 2009-03-04.