T4 conversion.... this is bugging me..

[Guest guest]

Hi all,

I just read yet again in someones post, that the doctor didn't want to increase

T4 in case it sent her hyperthyroid.

Normally your thyroid would make t4, which would circulate in your blood at a

given level and some t3. When you need some energy, you either use the t3 that

has been made by your thyroid, or you convert some of the T4 which is going

round your blood into t3. When you have the right amount of T4 stored in

your blood, the TSH drops and you don't make as much.

If you take levothyroxine, it circulates in your blood and when you have enough

the tsh drops. If you have too much, you make reverse t3 which breaks down the

excess t4 and gets rid of it.

So where, in taking too much levothyroxine would you be making too much t3,

which is what you have when you are hyper? Surely just having t4 in the blood

doesn't mean you automatically convert it to t3. ??? If you did convert

automatically then you'd be hyper as soon as you got any t4, t4 would always

show low in the blood and t3 would be high....

I just can't fathom how taking too much t4 could lead to hyper, there is

another step involved which tells your body to do the conversion to t3 when you

need it..... any ideas on this?