![]() ![]() The National Academy of Clinical Biochemistry (NACB) stated that it expected the reference range for adults to be reduced to 0.4–2.5 µIU/mL, because research had shown that adults with an initially measured TSH level of over 2.0 µIU/mL had "an increased odds ratio of developing hypothyroidism over the 20 years, especially if thyroid antibodies were elevated". In the UK, guidelines issued by the Association for Clinical Biochemistry suggest a reference range of 0.4–4.0 µIU/mL (or mIU/L). Reference ranges for TSH may vary slightly, depending on the method of analysis, and do not necessarily equate to cut-offs for diagnosing thyroid dysfunction. Applications Diagnostics įurther information: Thyroid function tests This is also the mechanism of trophoblastic tumors increasing the production of thyroid hormones. In pregnancy, prolonged high concentrations of hCG can produce a transient condition termed gestational hyperthyroidism. In addition, hCG shows some cross-reactivity to the TSH receptor and therefore can stimulate production of thyroid hormones. Stimulating antibodies to the TSH receptor mimic TSH and cause Graves' disease. (6) Secretion of thyroxine (T 4) and triiodothyronine (T 3) across the basolateral membrane of follicular cells to enter the circulation. (5) Stimulation of proteolysis of iodinated thyroglobulin to form free thyroxine (T 4) and triiodothyronine (T 3). (4) Increased endocytocis of the iodinated thyroglobulin protein across the apical membrane back into the follicular cell. This leads to the formation of thyroxine (T 4) and triiodothyronine (T 3) that remain attached to the thyroglobulin protein. (3) Stimulating the conjugation of iodinated tyrosine residues. (2) Stimulating iodination of thyroglobulin in the follicular lumen, a precursor protein of thyroid hormone. This occurs through stimulation of six steps in thyroid hormone synthesis: (1) Up-regulating the activity of the sodium-iodide symporter (NIS) on the basolateral membrane of thyroid follicular cells, thereby increasing intracellular concentrations of iodine (iodine trapping). Stimulation of the receptor increases T 3 and T 4 production and secretion. The TSH receptor is found mainly on thyroid follicular cells. The β chain has a 118-amino acid sequence.
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