Thyroid UK
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Thyroid binding globulin

When is it worth testing for Thyroid binding globulin (note: Not thyroglobulin). I am wondering if this could be implicated in why I cant seem to respond to a high dose of T3.

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What do you think might be happening with respect to TBG? Do you think yours is high? Low? Variable?

I am sorry but I cannot remember what you have had tested - a first stab at seeing the effect TBG is having can be seen if you have both Free T3 and Total T3 tested as the same time. More or less, the difference is how much is bound (largely to TBG but I think some also binds to albumin and transthyretin).

Rod

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Thanks helvella

My free T3 is high as I am on T3 only. My issue is that I am not responding to a very high dose of T3 only and am trying to figure out why.

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That is, as you say, a high dose!

Did I post this link for you?:

thyroidmanager.org/chapter/...

It says more than I know about these issues. Is your FT3 very high? Or only towards the top end? I agree the first thing is to decide if it is a matter of absorption - or of what happens once it has been absorbed.

Rod

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helvella, i cant seem to open the link but thank you. I will try when I get back to my home computer.

My free T3 is 6.2 (i think 4.2 is the upper limit of normal on that). The reason I checked it was to make sure that I was absorbing from the gut. I clearly am as the RT3 is low and the FT3 is high but clearly it is NOT getting into the cells or doing what it needs to do in there and I dont know HOW to check for that.

I dont think this is inherited, but rather acquired as I didnt have the inital high TH levels often associated with gene mutations. Rather it is peripheral or cellular resistance.

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Are you in the UK and what brand of T3 are you taking? I'm asking as I wonder if the medication is good quality. If I remember from an earlier post you allowed 24 hours between the last dose of T3 and taking the blood. In which case your 'real' fT3 figure would be around 10 or 12 after allowing for a half-life of a day or two. This would still be a bit low (if you were taking 120 mcg?) unless you are quite large. T3 is normally absorbed very easily, unlike T4 which is a larger molecule.

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jim111,

I did wait 48 hours for the test and am now on 270 mcg. I was wondering about absorption which is why I did the bloods to check. It showed RT3 as suppressed at 4.2 (9-27) which is to be expected and the freeT3 at 6.2. I am in the USA and am taking one that is compounded by the pharmacy as it is cheaper than getting cytomel. I am quite small, not large at all, at 114 lbs. Given that information, do you have any thoughts?

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It's difficult to measure fT3 if you are on L-T3. If you wait too long then most of it has disappeared from your blood, if it's too soon you can get silly numbers. I'd have the blood taken about 12 hours after the last dose and then add about 20% to get a very rough number. I would be temped to try Cytomel for a while as it's an established drug with a track record. This would show if there is a problem with your compounded form. If you do try Cytomel start on a lower dose, maybe 100 mcg, just in case your existing tablets are not quite right.

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