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CLA: THYROID SCREEN
THYROID GLAND
The thyroid gland in humans is a small, butterfly-shaped hormone-producing organ located in the neck on the front side of the trachea (“windpipe”), just below the larynx (“voice box”). It normally produces thyroxin (“T4” or tetraiodothyronine) and smaller amounts of triiodothyronine (or “T3”). The thyroid gland requires iodine in the diet to make these hormones. T4 and T3 are involved in metabolism of every cell in our bodies- their presence causes cellular metabolism to speed up and their absence causes it to slow down. Too much T4 or T3 causes hyperthyroidism (over-active) and too little causes hypothyroidism (under-active).
The function of the thyroid -- the making of these hormones -- is controlled by the pituitary gland, a pea-sized gland at the base of the brain, and specifically by a hormone it produces called thyroid stimulating hormone (TSH or thyrotropin). A chemical (called a “releasing factor”) coming from the adjacent brain tissue “tells” the pituitary gland to release TSH, which in turn “tells” the thyroid gland in the neck to make more T4 and T3. As the T4 and T3 levels rise and fall, the brain senses the levels and sends more releasing factor to the pituitary gland to start the process again. Measuring the blood TSH level is a very sensitive way to evaluate this process.
TEST RESULTS
If the TSH test result is above the reference range (the range in which most normal people’s hormone levels are found), this suggests the condition of hypothyroidism, or possibly too little iodine in the diet. If the TSH level is below the reference range, this can be normal, is occasionally related to hypothyroidism, but is more usually seen in hyperthyroidism (over-active thyroid) or with inflammation of the thyroid gland called thyroiditis. In any of the above circumstances, an abnormal TSH level will require further lab tests and an evaluation by a physician.
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