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question on bloodwork

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Old 02-07-2005, 02:05 PM   #1
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question on bloodwork

Just a quick question. My doctor has been treating my hypothyroidism based on TSH levels alone. Thanks to this board, I now know how important it is to check free T3 and free T4 levels as well. My Dr. was fine with this but I just got my lab slip in the mail today and it's checked off for TSH, T4 free and T3 total. Is the T3 total the same as free T3? The only other T3 option there is T3 uptake. Should he have checked that instead? He's my primary care physician. After a bad experience with the only endo. in the area, he's been helping manage my meds but I don't know how much experience he has with this and just want to make sure I'm getting the right thing tested.


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Old 02-07-2005, 06:22 PM   #2
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Re: question on bloodwork

The total is different from the free. T3 uptake is different as well. It sounds like he would have to write in the free T3 test, since it's not listed on the standard sheet.

Old 02-07-2005, 08:27 PM   #3
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Re: question on bloodwork

There are two ways T3 appears in the bloodstream. A portion of it is bound up in a protein that must be stripped off before the T3 can be absorbed by the cells. The other portion is "free", and readily usable by the cells. There is no way to know how much is bound and unusable if only the total T3 is measured. That's why it's preferable and more informative to measure only the free T3.

T3 uptake actually has nothing at all to do with the amount of T3 in the blood.

If there's an "other" blank at the bottom of the lab requisition form, fill in free T3. It's still possible that the lab in question doesn't even run the test, but it's worth a try.

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