When your body produces T3, a significant portion of it is soon bound by a protein in the blood and made unusable.
A Free T3 measures the amount of unbound, available T3 that is in your blood.
A total T3 test does not measure your T3 at all. The test result is derived by measuring your Total T4(which is a bad test) and doing a mathematical calculation to arrive at a value for Total T3. The description I provide may not be completely acurate, but it is close.
You can read about the total T3 test by going to the health pages and following the link in the thread "What do these blood tests mean?".
A Total T3 test measures both the bound and the available T3 in your blood. But it does not distinguish between the two. It just gives you a total count. What you need to know is how much Free T3 you have floating around.
A T3 uptake test is the test that I was reffering to, and I described it all wrong as well.
So I was wrong several different ways in my first post.
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