Answer: TSH, which stands for Thyroid Stimulating Hormone, is a chemical hormone produced by the pituitary gland that finely regulates the manufacture of thyroid hormones by the thyroid gland. The pituitary gland senses, in a very precise way, the levels of thyroid hormones in the blood stream at every single time and depending on these levels, the pituitary will adjust the release of TSH.
If the thyroid gland, for any reason, becomes sluggish and produces less thyroid hormone, this is immediately sensed by the pituitary, and the TSH released by the pituitary will automatically increase. The rise of TSH in the blood stream makes the thyroid gland increase the production of thyroid hormone back up to normal. Even in situations where there is a minute deficit of thyroid hormone caused by a damaged thyroid gland or deficiency of iodine, the pituitary reacts swiftly and the TSH increases in an obvious manner, even though the deficit of thyroid hormone is not detected through the testing of thyroid hormone levels.
This is the reason why TSH testing, done from a blood specimen using very sensitive techniques, is the most sensitive way of detecting hypothyroidism. The same thing happens with excess thyroid hormone. Imagine your thyroid gland is being stimulated by the immune system, such as in Graves’ disease, to produce excessive amounts of thyroid hormone. The first thing that happens, is a significant drop of TSH levels in the blood stream as a result of shut down of pituitary release of TSH.
Conventionally, normal thyroid function has been defined by what is viewed as a normal range for TSH levels. A few years ago, a normal range for TSH was considered to be 0.4 to 4.5 mIU/ml. However, there are many people with a bona fide Hashimoto’s thyroiditis and low grade hypothyroidism who have a TSH interpreted as normal because of this wide range of normalcy. Conventional medicine has struggled over the years to define what should be the upper cut off of normal TSH levels and this struggle has to do with the grey zone of normalcy of any kind of laboratory testing. It has been my view for the past 25 years that the normal range for TSH should be narrowed down to 0.4 to 2 mIU/ml. Medical associations have fortunately decreased the upper cut off to 3 mIU/ml.
I personally look at a TSH level above 1.8 mIU/ml as suspicious for low grade hypothyroidism. For people who take thyroid medications to treat their hypothyroidism, it is important to avoid over dosing, which will show up as a TSH less than 0.4 mIU/ml, and try to keep the TSH level less than 1.5 mIU/ml to minimize the likelihood of thyroid hormone deficit.
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