What is difference between total t3 and free t3

[Fionna]

which is a better test total t3 or free t3 and what is the difference

[Fionna]

Thanks for all the info. I did ask my Doc for a free t3 and he refused. So I am going to find another Doc

[AR-10]

I need to correct myself.

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.

But You want to ask for a Free T3.

[AR-10]

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?".

So ask for a Free T3. :-)

[cotubic1767]

Thank you for correcting your mistake in which you describe the T3 test.  Apparently the explanation refers to the T3 Uptake (or T4) test.  This was quite interesting to know, even though it did not address the question on the differences between a Total3 and Free3 test.  The T3 Uptake test does not measure any kind of T3 per se, as I understand you.  It seems that it is more about the ability of your body to convert T4 reserves to T3, which might be either Free T3 or Bound T3.  The total T3 represents both types of T3, after T4 is converted from T3 and so the Total T3 is typically the most common test.  This might be just enough info for many patients but if there is not enough bioactive (Free) T3 it does it matter what the Total T3 is?  We must know the Free T3 to determine the health factors involved.  The Free T3 is the clinical determinate of thyroid function as it is what many body cells use to establish metabolic functions, it appears.  The Free T3 is the "active" form of your thyroid hormone.  Total T3 includes the active form of T3 and inactive form of it.  So, the inactive form is bound to certain proteins and cannot be used to signal an increase in the rates of metabolism, which is one of the main functions of your thyroid gland!  Your TSH may be high, T4 may be high, but if a final conversion to T3 is mostly bound up by these Globulin Binding Proteins the net result is low thyroid function.  At least that is what this seems to mean to me from various reports on the internet.  The Uptake T3 was a missing part of the puzzle, so even though you meant to clarify something different, you were actually a bit of help, regarding the conversion from T4 Thyroxine to T3.  Most physicians test for T4, after prescribing thyroxine supplements (T4), but without checking on T3, it may be impossible for us to know if the body is converting the prescription drug to an active form that can be used alongside of the naturally occurring, iodothyronine or Free t3.