Produced by the pituitary gland, and stimulates the thyroid to produce T4 and T3.
Levels should be checked in adults at age 35 and every 5 years thereafter, particularly, in women and patients with concomitant autoimmune disease.
Clinical hyperthyroidism suppresses TSH levels to <0.1 mcU/mL.
TSH levels typically fall between 0.4 and 4.0 milliunits per liter (mU/L)
Thyrotropin is required to stimulate iodine uptake into follicular cells.
Thyrotropin controls all aspects of thyroid hormone synthesis and release.
Secretion of thyrotropin is stimulated by thyrotropin releasing hormone and inhibited by negative feedback through thyroid hormone.
High levels of thyrotropin in women during pregnancy has been associated with impaired cognitive development in their offspring, but antenatal thyroid screening for maternal hypothyroidism did not result in improved cognition in children at age 3 years (Lazarus JH et al).
Thyrotropin-receptor antibodies activate thyrotropin receptors in Graves’ disease, allowing the radioiodine to concentrate within the entire gland.
Plasma levels may be suppressed by severe non thyroidal disease, use of dopamine, high dose glucocorticoids, and levels < 0.1 mcU/mL may be seen in approximately 10% of intensive care unit patients.
When assessing thyroid function, thyroid hormone levels, especially, free thyroxine (FT4) levels consistently show stronger associations with a wide array of clinical conditions than the measurement of thyroid stimulating hormone (TSH), according to a systematic review and meta-analysis of more than 50 studies.
TSH values may be altered by corticosteroids, and dopamine, hypothalamic, and pituiary hypofunction.
Serum TSH has a log-linear relationship with circulating thyroid hormone.
A two fold change in free thyroxine produces a 100 fold change in TSH.
A slight reduction in circulating thyroid hormone levels can result in an elevation TSH levels above the normal range.
Most common cause of elevated levels is autoimmune thyroid disease.
With age there is a shifting increased concentration of TSH (Surks MI).
In a study of 2290 community dwelling residents ages 70-79 with increased TSH levels and functionally mobile, and who were not taking thyroid medication: it was found that mild subclinical hypothyroidism was associated with better mobility(Simonsick EM).
TSH production may fall in hypophysitis, pituitary tumors, or pituitary apoplexy.
High doses of glucocorticoids can suppressed TSH releasing hormone and TSH concentrations.