To Your Health

The evaluation of thyroid status is one of the most formidable tasks in medicine

Q. The thyroid panel my doctor ordered for me showed everything on the low side of the normal range except TSH, which was on the high side of normal. I have a lot of symptoms of low thyroid function, which is why the test was ordered. What should I do next? Are these "normal ranges" trustworthy?

A. Evaluation of thyroid status is one of the most formidable tasks in medicine. Depending on the interpretation of the three fairly standard tests in a thyroid panel (T4, T3, and TSH), there are at least 12 other tests that might be needed to clarify a complex situation.

Basically the thyroid gland produces a hormone with four iodine atoms (T4) and scant amounts of another hormone with three iodine atoms (T3) in response to stimulation by a hormone from the pituitary gland (TSH). These thyroid hormones, principally T3, affect weight loss or gain, energy level, skin condition, memory, heart rate, cholesterol levels, and menstrual regularity among other body functions. Think of the thyroid gland as the "cruise control" for your body. Thyroid hormones keep the body working at the right speed, neither too slow nor too fast. Among the nutrients, besides iodine and L-tyrosine that make up the thyroid molecule, the body needs selenium to convert T4 to T3. In America, iodine and L-tyrosine deficiencies are rare, but selenium deficiency is common, especially in certain parts of the country, and might account for a general low level of T4 and T3. Consider using a selenium supplement for about six weeks, decide whether you feel better, and maybe ask for the panel again.

Borderline abnormal test results may not attract your physician's attention, but when the levels of one or more of the three standard test components are clearly abnormal, your physician should begin a search for the reason for disruption of the system. TSH from the pituitary gland sets the "cruise control" in the thyroid gland, but the pituitary gland gets its orders from the hypothalamus, so a test of the signal (TRH) from the hypothalamus may be needed. The thyroid hormones, once produced, are carried to body cells by specific proteins such as TBG, which can be measured. There are also ways to judge how much of the two thyroid hormones are "free" and thus available to act, because as long as they are bound to transport proteins the hormones are inactive. There may even be detectable antibodies to the hormones that will interfere with their function. If there is any suspicion of thyroid cancer, a scan involving the use of radioactive iodine may be required. Each of these tests will help your doctor confirm or rule out certain diagnoses.

The most controversial test in the thyroid panel is TSH. According to the American Association of Clinical Endocrinologists the normal range for the TSH test should be changed to a lower and narrower range, 0.3 to 3.0 instead of 0.5 to 5.0. The new normal range is still extraordinarily broad, equivalent to setting the normal range for blood cholesterol at 30 to 300. Some doctors believe that unless TSH is between 1 and 2, well inside both the lower and higher end of "normal," women especially don't feel well and can't lose weight or get rid of other hypothyroidism symptoms.

The best doctor is the one who trusts you to accurately report on your experience with thyroid replacement and manages your thyroid condition with a combination of testing and your report on how you feel.

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