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TESTS AND DRUGS
Under construction is a page describing the various drugs used for the treatment of thyroid disease (click on Drugs at left):
Normally, the thyroid gland pumps enough thyroid hormone into the blood to cover all of the bodyís needs. Thyroid hormones include T4 (tetraiodothyronine, thyroxine) and T3 (triiodothyronine). T4 and T3 circulate in the blood primarily bound or linked to protein molecules. Thyroid carrier proteins include thyroxine binding globulin (TBG), albumin, or transthyretin (TTR). Linked to these proteins, thyroid hormone isnít available to the bodyís cells. Measurement of this protein bound thyroid hormone is referred to as a "total" level. Total T4 and to a lesser extent total T3 levels are affected by the concentrations of protein in the blood. Certain medications, hormones such as estrogen, other non-thyroidal illnesses and liver problems can cause alterations in protein concentration. Influenced by protein alterations, the total T4 and T3 measurements may not accurately represent thyroid function.
The free or unbound portion (free T4 or FT4 and free T3 or FT3) more accurately represents what the bodyís true thyroid hormone levels are. Levels of free hormone represent the active hormone available to react with cell receptors in the body.
Certain circumstances, including stress, trauma, medications, infections, and temperature fluctuations change the amount of thyroid hormone required by the body. The hypothalamus in the brain ensures that normal levels are maintained via a negative feedback mechanism. The hypothalamus releases a hormone known as thyrotropin releasing hormone (TRH) when it detects low levels of thyroid hormone in the blood. TRH, in turn, causes the pituitary to release a hormone known as thyrotropin or thyroid stimulating hormone (TSH). As its name implies, TSH stimulates the thyroid gland to produce and release more thyroid hormone into the blood circulation.
When blood levels of thyroid hormone are low (in hypothyroidism), the pituitary produces and releases excess TSH, and blood levels of TSH rise above the normal range. In hyperthyroidism, a condition of excess blood thyroid hormone, the hypothalamus orders the pituitary to stop releasing TSH, and blood TSH levels are low, often suppressed to levels < 0.01 mIU/L.
Although TSH is considered a valuable indicator of thyroid function, its results can be misleading. TSH levels as a measurement of thyroid function were originally designed to detect chronic cases of hypothyroidism or hyperthyroidism. However, it generally takes 6 weeks for TSH levels to reflect the status of thyroid hormone in the blood. This is because TSH in normally released in a pulsatile fashion, peaking during the night, and the changes in response are subtle, with TSH gradually responding to excess or diminished thyroid hormone. In patients undergoing medication changes or who are undergoing treatment for hyperthyroidism, TSH levels may take many weeks to many months to reflect thyroid hormone changes.
Thus, patients with abnormal thyroid function or abnormal thyroid hormone levels may have normal TSH levels in the early stages of thyroid dysfunction and after medication and treatment changes. For this reason, a FT4 and/or FT3 determination is also recommended.
The thyroid gland produces primarily T4 with only scant amounts of T3. The majority of T3 present in the blood is produced by conversion of T4 to T3 in peripheral (away from the thyroid) tissue, primarily the liver. Selenium deficiency, certain medical disorders, and certain medications suppress the conversion of T4 to T3, and it is important that levels of FT3 be measured in patients exhibiting symptoms of hyperthyroidism and hypothyroidism and normal T4 results.
Reference ranges for laboratory tests are established by testing a segment of the normal population, generally hospital workers, and averaging their results. For thyroid patients undergoing treatment, there are flaws in comparing patient results to this reference range.
There is a recent trend to discount TSH results and treat patients on the basis of their actual free thyroid hormone levels or their symptoms.
The following reference ranges represent commonly used thyroid function reference ranges. However, ranges and units of measurement may vary from one laboratory to another. Patient results must be compared to the reference range of the appropriate testing facility.
Adult Reference Ranges:
T4 = 5.6-13.7 ug/dl (mcg/dl)
FT4 = 0.8-1.5 ng/dl
T3= 87-180 ng/dl
FT3 = 230-420 pg/d;
TSH = 0.4-4.5 mIU/L (mU/L)
Copyright, Elaine A. Moore, July, 2000.
Medical Treatments for Graves' Disease
Posted 4-14-00: Elaine Moore's excellent article on Current Medical Treatments for Graves'. Click here on Medical Treatments for Graves'.SHOULD WE SCRAP THE TSH TEST ENTIRELY?
Dr. David Derry thinks so. In this interview, he looks at the real
history of thyroid testing, and why he believes "the TSH [test]
needs to be scrapped and medical students taught again how to
clinically recognize low thyroid conditions." Find out more about
his provocative ideas and why he thinks it's time for a return to a
more valid way of diagnosing and treating thyroid disease.
Other notes: don't get scared when the doctor says things like:
FNA or Fine Needle Aspiration
Some people have reported problems following FNA, so I don't encourage anyone to have it done. However, there is always the concern that the problem with the thyroid might be cancer. Thyroid cancer is rare and usually doesn't spread to other body organs, but it is a concern.
Here is an eloquent description of what it's like to go through the procedure.
I just wanted to update you all, and especially for those that are