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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. The results are then reported as a ratio to normal serum.
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:
Due to the very low concentration of T 4 and T 3 in the blood, TBG is rarely more than 25% saturated with its ligand. Unlike transthyretin and albumin, TBG has a single binding site for T 4 /T 3. TBG is synthesized primarily in the liver as a 54-kDa protein. In terms of genomics, TBG is a serpin; however, it has no inhibitory function like many ...
D1, D2, and D3 regulate the levels of T4, T3, and rT3. Three primary deiodinases are responsible for thyroid hormone conversion and breakdown. Type 1 (D1) deiodinates T4 to the biologically active T3, as well as the hormonally inactive and possibly inhibitory rT3. [3] [5] Type 2 (D2) converts T4 into T3, and breaks down rT3. D3 produces rT3 ...
The saturation of binding spots on thyronine-binding globulin (TBG) by endogenous T 3 can be estimated by the triiodothyronine resin uptake test. The test is performed by taking a blood sample, to which an excess of radioactive exogenous T 3 is added, followed by a resin that also binds T 3.
"You can have a normal total testosterone level, but still suffer from symptoms of low T if your free testosterone is low," says Staheli. In fact, some research suggests that free T levels are a ...
They can also be measured as total T 3 and total T 4, which depend on the amount that is bound to thyroxine-binding globulin (TBG). [74] A related parameter is the free thyroxine index, which is total T 4 multiplied by thyroid hormone uptake, which, in turn, is a measure of the unbound TBG. [75]
Thyroglobulin (Tg) is a 660 kDa, dimeric glycoprotein produced by the follicular cells of the thyroid and used entirely within the thyroid gland. Tg is secreted and accumulated at hundreds of grams per litre in the extracellular compartment of the thyroid follicles, accounting for approximately half of the protein content of the thyroid gland. [5]