thyroid-stimulating hormone test


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thyroid

 [thi´roid]
2. pertaining to the thyroid gland.
4. a preparation of thyroid gland from domesticated food animals, containing levothyroxine and liothyronine and used as replacement therapy in the diagnosis and treatment of hypothyroidism and the prevention and treatment of goiter and thyroid carcinoma; administered orally.
thyroid crisis a sudden and dangerous increase of the symptoms of thyrotoxicosis, seen in patients with severe hyperthyroidism or in the period immediately following a thyroidectomy. (However, good postoperative care and the use of radioiodine ablation techniques have greatly reduced the incidence of this once common postoperative complication.) Called also thyroid or thyrotoxic storm.



Thyroid crisis is a serious event that can be fatal if not brought under control. All of the body processes are accelerated to dangerously high levels. The pulse may rise to 200 beats per minute, and there is concurrent rise in the respiratory rate. The temperature control center loses control, bringing about a rapid and steady increase in body temperature. Pulmonary edema and congestive heart failure can also occur.

Treatment is aimed at correction of the hyperthyroidism, control of the symptoms, and prevention of further crisis by treating the underlying cause. Medications are employed to block synthesis of thyroid hormones, block their release, and inhibit conversion of triiodothyronine to thyroxine. plasmapheresis. plasma exchange, or hemodialysis may be necessary to remove the hormones from the circulation.

Supportive care includes administration of oxygen and measures to control hyperthermia, such as the use of ice packs or a hyperthermia blanket. Intravenous hydration is important to prevent shock. The use of glucocorticoids is associated with improved survival rates. propranolol, sympatholytics, and guanethidine are often used, as well as other medications that treat symptoms.
thyroid function test a test of the functioning of the thyroid gland, such as its proper production of thyroid hormones. See radioiodineuptake test, thyroid-stimulating hormone test, thyrotropin-releasing hormone test, and triiodothyronine resin uptake test.
thyroid gland the largest of the endocrine glands, consisting of two lateral lobes connected by an isthmus; a third pyramidal lobe sometimes extends up from the isthmus. The thyroid gland is located in the front and sides of the neck just below the thyroid cartilage and produces hormones that are vital in maintaining normal growth and metabolism (see thyroid hormones). It also serves as a storehouse for iodine.



Diagnostic tests for thyroid disorders include radioimmunoassay for T3, T4, and thyroid-stimulating hormone (TSH), free thyroxine serum concentration, and free thyroxine index (FTI). These and other thyroid function tests can be distorted by preparations and foods containing iodine, and by oral contraceptives, phenytoin (Dilantin), and several other drugs. The thyroid scan is useful in detecting nodules and active thyroid tissue and, combined with radioactive iodine uptake, measures the ability of the thyroid gland to take in ingested iodine.

Persons who received radiation to the head and neck as children are at higher than normal risk for development of thyroid abnormalities. Of these disorders about one-third are carcinomas of the thyroid. Other problems related to radiation early in life include adenomas and other malignant and benign tumors, hypo- and hyperthyroidism, and thyroiditis. The American Thyroid Association suggests periodic laboratory testing and physical assessment of persons at high risk in order to detect these abnormalities when they are more amenable to treatment.
Thyroid gland.
thyroid hormones iodothyronines secreted by the thyroid gland, principally thyroxine (tetraiodothyronine or T4) and triiodothyronine (T3). The serum level of T4 is normally 45 to 50 times the level of T3. However, T3 is several times more active than T4, and most T3 is produced by metabolism of T4 in peripheral tissues. The pharmaceutical names for T4 and T3 are levothyroxine and liothyronine, respectively. Thyroid hormones influence many metabolic processes. They stimulate the cellular production of heat; stimulate protein synthesis; regulate many aspects of carbohydrate metabolism; stimulate lipid synthesis, mobilization, and degradation; stimulate the synthesis of coenzymes from vitamins; and may affect the response of tissues to epinephrine and norepinephrine.



Secretion of thyroid hormones is regulated by the hypothalamus-pituitary-thyroid control system. Internal environmental conditions, such as low thyroid hormone and norepinephrine serum levels, or external factors, such as cold and stress, activate the hypothalamus, which secretes thyrotropin-releasing hormone (TRH). This hormone acts on the pituitary gland and brings about the release of thyroid-stimulating hormone (TSH). The TSH then stimulates the release of thyroid hormones such as T3 and T4 from the thyroid gland. When sufficient levels of serum thyroxine and other thyroid hormones have been reached, there is negative feedback to the hypothalamus and TRH is no longer secreted. See also hypothyroidism and hyperthyroidism.
thyroid-stimulating hormone test a thyroid function test in which thyrotropin (thyroid-stimulating hormone) is administered intramuscularly and the thyroid gland is monitored over time with scintiscanning or radioimmunoassays for a response or areas of decreased responsiveness. Called also TSH test and TSH stimulation test.

thyroid-stimulating hormone test (TSH test)

a thyroid function test in which thyrotropin (thyroid-stimulating hormone) is administered intramuscularly and the thyroid gland is monitored over time with scintiscanning or radioimmunoassays for a response or areas of decreased responsiveness. It is also used to monitor exogenous thyroid replacement. The test was formerly used for determining whether hypothyroidism was caused by thyroid gland failure or by deficiency in thyrotropin. Also called thyroid-stimulating hormone assay.
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