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003444. [ edit on Wikidata] Thyroid function tests ( TFTs) is a collective term for blood tests used to check the function of the thyroid. [ 1] TFTs may be requested if a patient is thought to suffer from hyperthyroidism (overactive thyroid) or hypothyroidism (underactive thyroid), or to monitor the effectiveness of either thyroid-suppression ...
The therapeutic target range TSH level for patients on treatment ranges between 0.3 and 3.0 μIU/mL. [18] For hypothyroid patients on thyroxine, measurement of TSH alone is generally considered sufficient. An increase in TSH above the normal range indicates under-replacement or poor compliance with therapy.
In addition to testing the TSH levels, many doctors test for T 3, Free T 3, T 4, and/or Free T 4 for more detailed results. Free T 4 is unbound to any protein in the blood. Adult limits for these hormones are: TSH (units): 0.45 – 4.50 uIU/mL; T 4 Free/Direct (nanograms): 0.82 – 1.77 ng/dl; and T 3 (nanograms): 71 – 180 ng
The major form of thyroid hormone in the blood is thyroxine (T 4), whose half-life of around one week [4] is longer than that of T 3. [5] In humans, the ratio of T 4 to T 3 released into the blood is approximately 14:1. [6] T 4 is converted to the active T 3 (three to four times more potent than T 4) within cells by deiodinases (5′-deiodinase).
The initial diagnostic evaluation will start with plasma thyroid-stimulating hormone (TSH) concentration. [16] If elevated, it signifies hypothyroidism. [16] The elevation is usually a marked increase over the normal range and is generally greater than 20 mg/dl. [18] Free T4 levels will usually be lowered, but sometimes might be normal. [58]
Thyroid's secretory capacity ( GT, also referred to as thyroid's incretory capacity, maximum thyroid hormone output, T4 output or, if calculated from serum levels of thyrotropin and thyroxine, as SPINA-GT[ a]) is the maximum stimulated amount of thyroxine that the thyroid can produce in a given time-unit (e.g. one second). [ 2][ 3]
Free T4 and total T3 can be measured when hyperthyroidism is of high suspicion as it will improve the accuracy of the diagnosis. Free T4, total T3 or both are elevated and serum TSH is below normal in hyperthyroidism. If the hyperthyroidism is mild, only serum T3 may be elevated and serum TSH can be low or may not be detected in the blood. [14 ...
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 ] [ 44 ] 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 ...