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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.
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.
Reference ranges (reference intervals) for blood tests are sets of values used by a health professional to interpret a set of medical test results from blood samples. Reference ranges for blood tests are studied within the field of clinical chemistry (also known as "clinical biochemistry", "chemical pathology" or "pure blood chemistry"), the ...
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 ...
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 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/dl.
The TSH, in turn, stimulates the thyroid to produce thyroid hormone until levels in the blood return to normal. Thyroid hormone exerts negative feedback control over the hypothalamus as well as anterior pituitary, thus controlling the release of both TRH from hypothalamus and TSH from anterior pituitary gland.
The remainder of the serum cholesterol after subtracting the HDL is the non-HDL cholesterol. The concentration of these other components, which may cause atheroma, is known as the non-HDL-C. This is now preferred to LDL-C as a secondary marker as it has been shown to be a better predictor and it is more easily calculated. [10]