The other 20 is triiodothyronine measured as T3 by RIA. Sometimes the diseased thyroid gland will start producing very high levels of T3 but still produce normal levels of T4. Therefore measurement of both hormones provides an even more accurate evaluation of thyroid function.
It has also been found that thyroid nodules that concentrate iodine are rarely cancerous; this is not true if the scan is done with technetium. Therefore, all scans are now done with radioactive iodine.
This "TRH test" is presently the most sensitive test in detecting early hyperthyroidism. Patients who show too much response to TRH (TSH rises greater than 40) may be hypothyroid. This test is also used in cancer patients who are taking thyroid replacement to see if they are on sufficient medication.
Iodine Uptake Scan A means of measuring thyroid function is to measure how much iodine is taken up by the thyroid gland (RAI uptake). Remember, cells of the thyroid normally absorb iodine from our blood stream (obtained from foods we eat) and use it to make thyroid hormone (described on our thyroid function page ).
Some information on this page is a little more advanced. If you have trouble understanding the process of normal thyroid function, please go to our page describing this process first. As we have seen from our overview of normal thyroid physiology, the thyroid gland produces T4 and T3.
Measurement of Serum Thyroid Hormones: T3 by RIA. As stated on our thyroid hormone production page, thyroxine (T4) represents 80 of the thyroid hormone produced by the normal gland and generally represents the overall function of the gland.
Thyroid Binding Globulin Most of the thyroid hormones in the blood are attached to a protein called thyroid binding globulin (TBG). If there is an excess or deficiency of this protein it alters the T4 or T3 measurement but does not affect the action of the hormone.
TRH Test In normal people TSH secretion from the pituitary can be increased by giving a shot containing TSH Releasing Hormone (e hormone released by the hypothalamus which tells the pituitary to produce TSH).
Intellectual disability may occur if a baby's thyroid gland does not produce enough thyroid hormone (congenital hypothyroidism ). Older children also need thyroid hormones to grow and develop normally, and adults need the hormones to regulate the way the body uses energy ( metabolism ).
Of course, patients who are taking thyroid medication will not take up as much iodine in their thyroid gland because their own thyroid gland is turned off and is not functioning.
Pregnant women should not have thyroid scans performed because the iodine can cause development troubles within the baby's thyroid gland. Two types of thyroid scans are available. A camera scan is performed most commonly which uses a gamma camera operating in a fixed position viewing the entire thyroid gland at once.
You may need to stop taking certain drugs temporarily before the test to help ensure accurate results. Medications that can affect your T4 levels include: drugs including hormones, such as androgen, estrogen, birth control pills drugs designed to affect your thyroid or treat thyroid conditions some drugs designed to treat cancer steroids.
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