I've seen a few posts on here where people wondered whether they were 'pooling', but I don't understand what that means. I did google it (pooling, thyroxine) but not much joy, same deal with a search on HU. Can anybody clarify?
Thanks
What is 'pooling'?: I've seen a few posts on here... - Thyroid UK
What is 'pooling'?
Written by
hose1975
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Basically pooling comes about if T4 (thyroxine) is not converting to T3, which is the active hormone your body needs.
In this case you get a high FT4 reading and a low FT3 reading because of the non-conversion and you will have symptoms because of the low FT3. TSH will be low, because the pituitary picks up the high level of T4 in the blood.
The problem comes if you don't have an FT3 result. If the doc just has a low TSH and high FT4 result, they often assume the patient is over-medicated, which just makes things worse.
Does that help?
It certainly does! Many thanks. I don't think it's a conversion problem for me (last TSH 0.04 (0.5-5.5), fT4 18 (10-19.9), fT3 3.2 (2.2-3.6). Just baffled as to why I'm so knackered and displaying more bloody hypo symptoms after starting on ferrous fumarate (taken well away from my thyroid meds).
I know this was a long time ago, but if someone reads it and wants an answer... You can have high free T3 and still have tissue level hypothyroidism. A high deiodinase 3 (D3) level which converts T4 into reverse T3 (rT3) and T3 into T2 can convert T3 inside the cells to T2, BEFORE the T3 has had time to bind to its receptor. So you can have a high blood serum free T3 in tests but still have hypothyroidism if your D3 is too high for your body. There is no accessible test for D3, but if you get an rT3 test and it is higher than it should be that is the only current way to assess for high D3. I had this, was on 200mcg of T4 and 20mcg of T3 and I lowered my T4 dose immediately to 50mcg of T4 per day and increased my T3 to 40. I'm still working on it but high D3 is triggered by your own body's decision of the level of T4 and T3 being too high, it's commonly triggered when T4 medication is too high. The other way to overcome it is by taking huge amounts of T4 to overwhelm your own body's highest production of D3, you're probably better to lower it though.
Also anyone reading this look into things that are known to lower rT3, and think of rT3 as being the canary in the mine. Also, as I've heard this a lot, rT3 does NOT bind to T3 receptors or block them. It's high D3 that is the problem, and yes, it increases rT3.
It is a seven year old thread you have posted on!
Doesn't make it invalid and it is not wrong to do so, but maybe not so relevant? That rT3 doesn't block T3 receptors has been discussed many times more recently.
You can see about the D3 here, 9gurus.com/how-deiodinase-e...
