I am sure somebody has posted this already, but I can't seem to find it.
I have a friend who is getting her thyroid checked out now, and she wanted to know what exactly the Free T3, Free T4, and TSH tests are and what they do/look for.
I thought maybe somebody here could explain better than I could.
In short -
The TSH test measures the blood level of the hormone which is made by the pituitary gland that signals the thyroid gland to manufacture its own hormones, T4 and T3. A higher TSH indicates an underactive thyroid gland; a low value indicates an overactive gland.
FT4 and FT3 tests measure the level of the "free" thyroid hormones in the blood... those which are unbound to proteins and are thus available to the body's cells for absorption.
It's a complex interaction of hormones. I'd suggest she borrow a basic thyroid book from her library to find a good layman's explanation of thyroid function, malfunction, and diagnosis. Hope that helped a little, at least.
[This message has been edited by midwest1 (edited 09-17-2003).]