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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 therapy.
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]
Initial blood tests often include thyroid-stimulating hormone (TSH) and free thyroxine (T4). [9] Total and free triiodothyronine (T3) levels are less commonly used. [9] If autoimmune disease of the thyroid is suspected, blood tests looking for Anti-thyroid autoantibodies can also be obtained. Procedures such as ultrasound, biopsy and a ...
Hypothyroidism is diagnosed by looking at the free thyroxine (T4) levels in people with elevated TSH levels, and comparing the ratio between them. People with high TSH and low T4 get a diagnosis ...
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
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.
Blood free thyroxine and TSH levels are monitored to help determine whether the dose is adequate. This is done 4–8 weeks after the start of treatment or a change in levothyroxine dose. Once the adequate replacement dose has been established, the tests can be repeated after 6 and then 12 months, unless there is a change in symptoms. [8]
In such a case a TRH stimulation test, in which TRH is given and TSH levels are measured at 30 and 60-minutes after, may be conducted. [84] T 3 and T 4 can be measured directly. 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 ...