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TSHB
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12372
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1
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p
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13
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188540
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7252
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NM_000549
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P01222
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(also known as '''TSH''' or '''thyrotropin''') is a hormone synthesized and secreted by
Thyrotrope cells in the
Anterior Pituitary Gland which regulates the endocrine function of the
Thyroid Gland .
1
TSH stimulates the thyroid gland to secrete the hormones
Thyroxine (T4) and
Triiodothyronine (T3). TSH production is controlled by a Thyrotropin Releasing Hormone, (
TRH ), which is manufactured in the hypothalamus and transported to the Anterior Pituitary gland, 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 .
TSH is a glycoprotein and consists of two subunits, the ''alpha'' and the ''beta'' subunit.
The
TSH Receptor is found mainly on thyroid
Follicular Cells Parmentier M, Libert F, Maenhaut C, Lefort A, Gérard C, Perret J, Van Sande J, Dumont JE and Vassart G., Molecular cloning of the thyrotropin receptor, Science 246 (1989), 1620-1622. 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 .
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 0.3 and 3.0
U IU /mL (equivalent to
M IU/L), but 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 to during childhood and puberty to adult levels, 0.4-4.0 uIU/mL.
2 - see ''Section 2. Pre-analytic factors''
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
{Link without Title} 20 years, especially if thyroid antibodies were elevated".
3 - see ''Section 3.C.Thyrotropin/ Thyroid Stimulating Hormone (TSH) measurement
Clearly, both TSH and T3 and T4 should be measured to ascertain where a specific thyroid disfunction 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.
