From what I understand, TSH (Thyroid Stimulating Hormone) has for purpose
to stimulate the thyroid to produce thyroxine. Depending on the quality
of function of the thyroid, more or less TSH will be needed: If the
thyroid produces very little T4, the pituitary gland produces more TSH.
The opposite is true, the more the thyroid is able to produce T4, the
less the pituitary will have to send out its TSH... "

Low level THS tends to show high thyroid function.
High level THS tends to show low thyroid function.

I have Hashimoto's. My endo increase my dosage of Synthroid according to
the level of THS. Right now my TSH is in the high side of normal. She
plans on increasing the dosage of synthroid until my TSH is in the lower
side of normal.

Jacquie