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Subclinical hypothyroidism (SCH) is present when the TSH is high but the T4 level is in the normal range but usually low normal. SCH is the commonest form of hypothyroidism in pregnancy and is usually due to progressive thyroid destruction due to autoimmune thyroid disease. [citation needed]
Affected patients may have normal, low, or slightly elevated TSH depending on the spectrum and phase of illness. Total T4 and T3 levels may be altered by binding protein abnormalities, and medications. Reverse T3 levels are generally increased, while FT3 is decreased. FT4 levels may have a transient increase, before becoming subnormal during ...
TSH values may also be lower than normal (particularly in the first trimester) and the normal range should be adjusted for the stage of pregnancy. [ 8 ] [ 43 ] In pregnancy, subclinical hypothyroidism is defined as a TSH between 2.5 and 10 mIU/L with a normal thyroxine level, while those with TSH above 10 mIU/L are considered to be overtly ...
A suppressed TSH could represent the hyperthyroid phase, but warrants further testing to investigate for possible Graves' disease. [6] A normal TSH with persistent symptoms could represent the shift between phases and requires repeat testing 4–6 weeks later; an elevated TSH at this time could indicate the hypothyroid phase. [6]
Thyroid hormones, T4 and TSH, diffuse across the placenta traveling from the mother to fetus for 10–12 weeks before the fetus’s own thyroid gland can begin synthesizing its own thyroid hormones. [2] The mother continues to supply some T4 to the fetus even after he/she is able to synthesize his/her own.
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]
Elevated reverse T 3 (RT 3) together with low-normal TSH and low-normal T 3, T 4 values, which is regarded as indicative for euthyroid sick syndrome, may also have to be investigated for chronic subacute thyroiditis (SAT) with output of subpotent hormones. Absence of antibodies in patients with diagnoses of an autoimmune thyroid in their past ...
Congenital hypothyroidism can also occur due to genetic defects of thyroxine or triiodothyronine synthesis within a structurally normal gland. Among specific defects are thyrotropin ( TSH ) resistance, iodine trapping defect, organification defect, thyroglobulin , and iodotyrosine deiodinase deficiency.