Thyroid-stimulating hormone
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| Thyroid-stimulating hormone, alpha (Glycoprotein hormones, alpha polypeptide)
| |
| Identifiers | |
| Symbol | CGA |
| Alt. Symbols | HCG, GPHa, GPHA1 |
| Entrez | 1081 |
| HUGO | 1885 |
| OMIM | 118850 |
| RefSeq | NM_000735 |
| UniProt | P01215 |
| Other data | |
| Locus | Chr. 6 q14-q21 |
| Thyroid-stimulating hormone, beta
| |
| Identifiers | |
| Symbol | TSHB |
| Entrez | 7252 |
| HUGO | 12372 |
| OMIM | 188540 |
| RefSeq | NM_000549 |
| UniProt | P01222 |
| Other data | |
| Locus | Chr. 1 p13 |
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Thyroid-stimulating hormone (also known as TSH or thyrotropin) is a peptide hormone synthesized and secreted by thyrotrope cells in the anterior pituitary gland which regulates the endocrine function of the thyroid gland.[1]
Physiology
Controlling the rate of release
TSH stimulates the thyroid gland to secrete the hormones thyroxine (T4) and triiodothyronine (T3).[1] TSH production is controlled by a Thyrotrophin Releasing Hormone, (TRH), which is manufactured in the hypothalamus and transported to the anterior pituitary gland via the superior hypophyseal artery, where it increases TSH production and release. Somatostatin is also produced by the hypothalamus, and has an opposite effect on the pituitary production of TSH, decreasing or inhibiting its release.
The level of thyroid hormones (T3 and T4) in the blood have an additional effect on the pituitary release of TSH; When the levels of T3 and T4 are low, the production of TSH is increased, and conversely, when levels of T3 and T4 are high, then TSH production is decreased. This effect creates a regulatory negative feedback loop.
Subunits of TSH
TSH is a glycoprotein and consists of two subunits, the alpha and the beta subunit.
- The α (alpha) subunit (i.e., chorionic gonadotropin alpha) is identical to that of human chorionic gonadotropin (HCG), luteinizing hormone (LH), follicle-stimulating hormone (FSH).
- The β (beta) subunit is unique to TSH, and therefore determines its function.
The TSH receptor
The TSH receptor is found mainly on thyroid follicular cells[1]. Stimulation of the receptor increases T3 and T4 production and secretion.
Stimulating antibodies to this receptor mimic TSH action and are found in Graves' disease.
Diagnostic use
TSH levels are tested in the blood of patients suspected of suffering from excess (hyperthyroidism), or deficiency (hypothyroidism) of thyroid hormone. Generally, a normal range for TSH for adults is between 0.4 and 5.0 uIU/mL (equivalent to mIU/L), but values vary slightly among labs. The optimal goal TSH level for patients on treatment ranges between 0.3 to 3.0 mIU/L.[1]. The interpretation depends also on what the blood levels of thyroid hormones (T3 and T4) are. The National Health Service in the UK considers a "normal" range to be more like 0.1 to 5.0 uIU/mL.
TSH levels for children normally start out much higher. In 2002, the National Academy of Clinical Biochemistry (NACB) in the United States recommended age-related reference limits starting from about 1.3-19 uIU/mL for normal term infants at birth, dropping to 0.6-10 uIU/mL at 10 weeks old, 0.4-7.0 uIU/mL at 14 months and gradually dropping during childhood and puberty to adult levels, 0.4-4.0 uIU/mL.[1]
The NACB also stated that it expected the normal (95%) range for adults to be reduced to 0.4-2.5 uIU/mL, because research had shown that adults with an initially measured TSH level of over 2.0 uIU/mL had "an increased odds ratio of developing hypothyroidism over the [following] 20 years, especially if thyroid antibodies were elevated".[1]
| Source of pathology | TSH level | thyroid hormone level | Disease causing conditions |
| hypothalamus/pituitary | high | high | benign tumor of the pituitary (adenoma) or thyroid hormone resistance |
| hypothalamus/pituitary | low | low | hypopituitarism |
| thyroid | low | high | hyperthyroidism or Grave's disease |
| thyroid | high | low | congenital hypothyroidism (cretinism), hypothyroidism |
Clearly, both TSH and T3 and T4 should be measured to ascertain where a specific thyroid dysfunction is caused by primary pituitary or by a primary thyroid disease. If both are up (or down) then the problem is probably in the pituitary. If the one component (TSH) is up, and the other (T3 and T4) is down, then the disease is probably in the thyroid itself. The same holds for a low TSH, high T3 and T4 finding.
A TSH assay is now also the recommended screening tool for thyroid disease. Recent advances in increasing the sensitivity of the TSH assay make it a better screening tool than free T4.[1]
Therapeutic use
A drug, recombinant human TSH (rhTSH), called Thyrogen, is manufactured by Genzyme Corp. in Cambridge, Massachusetts. The rhTSH is used in patients with thyroid cancer which is related to tumoral factors.
Footnotes
External links
bs:Tireostimulišući hormoncs:Thyreotropní hormon da:TSH de:Thyreotropin dv:ތައިރޮއިޑް ސްޓިމިއުލޭޓިންގ ހޯރމޯންfr:Thyréostimuline id:Hormon Tirotrop it:Ormone tireostimolante he:תירוטרופין lt:Tireotropinas hu:Thyreoidea-stimuláló hormon mk:Тиреотропин nl:Thyroïdstimulerend hormoon ja:甲状腺刺激ホルモン no:Tyroideastimulerende hormonsk:Tyreotropín sr:Тиреостимулишући хормон fi:Tyreotropiini sv:Tyreoideastimulerande hormon
Acknowledgement and Attribution Regarding Sources of Content
Some of the initial content on this page may be incorporated in part from copyleft sources in the public domain including wikis such as Wikipedia and AskDrWiki. Drug information for patients came from the The National Library of Medicine. Infectious disease information may have come from the Centers for Disease Control (CDC). Differential Diagnoses are drawn from clinicians as well as an amalgamation of 3 sources: 1.The Disease Database; 2. Kahan, Scott, Smith, Ellen G. In A Page: Signs and Symptoms. Malden, Massachusetts: Blackwell Publishing, 2004:3; 3. Sailer, Christian, Wasner, Susanne. Differential Diagnosis Pocket. Hermosa Beach, CA: Borm Bruckmeir Publishing LLC, 2002:7 .
