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Total triiodothyronine (Total T 3) is rarely measured, having been largely superseded by free T3 tests. Total T3 is generally elevated in hyperthyroidism and decreased in hypothyroidism. [2] Reference ranges depend on the method of analysis. Results should always be interpreted using the range from the laboratory that performed the test.
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.
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 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. A fraction of the radioactive T 3 binds to sites on TBG not already occupied by endogenous thyroid hormone, and the remainder binds to the resin. The amount of labeled hormones bound to the resin is ...
T3 and T4 levels can thus be measured as free T3 and T4, or total T3 and T4, which takes into consideration the free hormones in addition to the protein-bound hormones. Free T3 and T4 measurements are important because certain drugs and illnesses can affect the concentrations of transport proteins, resulting in differing total and free thyroid ...
In 1968, a reduced T4 half-life in athletes was discovered. This was the first awareness of thyroid hormone concentration alterations that were not a result of thyroid gland or pituitary dysfunction. In 1971, they also found a transient increase in T4 during bicycle training. [2]
The TRH test involves administration of a small amount of TRH intravenously, [1] following which levels of TSH will be measured at several subsequent time points using samples of blood taken from a peripheral vein. [citation needed] The test is used in the differential diagnosis of secondary and tertiary hypothyroidism.
De Quervain thyroiditis is diagnosed through clinical and test results, with laboratory features including elevated C-reactive protein and erythrocyte sedimentation rate. Thyroid function testing often shows decreased thyroid stimulating hormone and increased serum levels of triiodothyronine and thyroxine during the acute phase.