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Thyroid-stimulating hormone (also known as thyrotropin, thyrotropic hormone, or abbreviated TSH) is a pituitary hormone that stimulates the thyroid gland to produce thyroxine (T 4 ), and then triiodothyronine (T 3) which stimulates the metabolism of almost every tissue in the body. [ 1] It is a glycoprotein hormone produced by thyrotrope cells ...
Thyroid hormones are any hormones produced and released by the thyroid gland, namely triiodothyronine ( T3) and thyroxine ( T4 ). They are tyrosine -based hormones that are primarily responsible for regulation of metabolism. T 3 and T 4 are partially composed of iodine, derived from food. [ 2] A deficiency of iodine leads to decreased ...
003444. [ edit on Wikidata] Thyroid function tests ( TFTs) is a collective term for blood tests used to check the function of the thyroid. [ 1] TFTs may be requested if a patient is thought to suffer from hyperthyroidism (overactive thyroid) or hypothyroidism (underactive thyroid), or to monitor the effectiveness of either thyroid-suppression ...
Subclinical hypothyroidism is a biochemical diagnosis characterized by an elevated serum TSH level, but with a normal serum free thyroxine level. [ 48 ] [ 49 ] [ 50 ] The incidence of subclinical hypothyroidism is estimated to be 3-15% and a higher incidence is seen in elderly people, females and those with lower iodine levels. [ 48 ]
TSH levels are determined by a classic negative feedback system in which high levels of T3 and T4 suppress the production of TSH, and low levels of T3 and T4 increase the production of TSH. TSH levels are thus often used by doctors as a screening test, where the first approach is to determine whether TSH is elevated, suppressed, or normal. [25]
The TSH, in turn, stimulates the thyroid to produce thyroid hormone until levels in the blood return to normal. Thyroid hormone exerts negative feedback control over the hypothalamus as well as anterior pituitary, thus controlling the release of both TRH from hypothalamus and TSH from anterior pituitary gland. [2]
They may reveal hyperthyroidism (high T 3 and T 4), hypothyroidism (low T 3, T 4), or subclinical hyperthyroidism (normal T 3 and T 4 with a low TSH). [ 84 ] TSH levels are considered the most sensitive marker of thyroid dysfunction. [ 84 ]
The initial diagnostic evaluation will start with plasma thyroid-stimulating hormone (TSH) concentration. [16] If elevated, it signifies hypothyroidism. [16] The elevation is usually a marked increase over the normal range and is generally greater than 20 mg/dl. [18] Free T4 levels will usually be lowered, but sometimes might be normal. [58]