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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 or hormone replacement ...
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]
Further information: Thyroid function tests. Triiodothyronine (T 3) and thyroxine (T 4) can be measured as free T 3 and free T 4, which are indicators of their activities in the body. [73] 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). [73]
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] Doctors may check thyroglobulin antibodies (TgAb) whenever a thyroglobulin test is performed to see if the antibody is interfering.
These normal hormonal changes often make pregnancy look like a hyperthyroid state but may be within the normal range for pregnancy, so it necessary to use trimester specific ranges for TSH and free T4. [23] [24] True hyperthyroidism in pregnancy is most often caused by an autoimmune mechanism from Graves' Disease. [23]
100-150. Test of. Sensitivity of TSH-producing pituitary cells to thyroid hormones; also a marker for the set point of thyroid homeostasis. The Thyrotroph Thyroid Hormone Sensitivity Index (abbreviated TTSI, also referred to as Thyrotroph T4 Resistance Index or TT4RI) is a calculated structure parameter of thyroid homeostasis.
However, as the two thyroid hormones travel bound to other molecules, and it is the "free" component that is biologically active, free T 3 and free T 4 levels can be measured. [84] T 3 is preferred, because in hypothyroidism T 3 levels may be normal. [ 84 ]
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.