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Thyroid hormone uptake (T uptake or T 3 uptake) is a measure of the unbound thyroxine binding globulins in the blood, that is, the TBG that is unsaturated with thyroid hormone. [2] Unsaturated TBG increases with decreased levels of thyroid hormones. It is not directly related to triiodothyronine, despite the name T 3 uptake. [2] Reference ranges:
Thyroid hormone binding ratio (THBR) is a thyroid function test that measures the "uptake" of T3 or T4 tracer by thyroid-binding globulin (TBG) in a given serum sample. This provides an indirect and reciprocal estimate of the available binding sites on TBG within the sample.
Finally, both hormones bind with a low affinity to serum albumin, but, due to the large availability of albumin, it has a high capacity. The saturation of binding spots on thyronine-binding globulin (TBG) by endogenous T 3 can be estimated by the triiodothyronine resin uptake test.
Thyroxine-binding globulin (TBG) is a globulin protein encoded by the SERPINA7 gene in humans. TBG binds thyroid hormones in circulation.It is one of three transport proteins (along with transthyretin and serum albumin) responsible for carrying the thyroid hormones thyroxine (T 4) and triiodothyronine (T 3) in the bloodstream.
The most useful marker of thyroid gland function is serum thyroid-stimulating hormone (TSH) levels. 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 ...
Fasting in healthy, euthyroid people causes reduced T3 and elevated rT3, although TSH is usually unchanged. [3] [5] [10] Even moderate weight loss can lower T3. [2] This may be primarily via reduced levels of leptin (the satisfaction hormone). Low leptin levels can downregulate hypothalamic TRH neurons and cause a reduction in TSH.