The range for TSH is (0.27-4.2). If both the free T's are so low why is my pituitary not signalling more? Shouldn't the TSH be much higher? Or does it not work like that?
I know normally in secondary that the TSH VERY low or almost non existent but why isn't mine higher?
I wasn't taking any meds when these bloods were taken by the way. I am now back on my NDT.
I know this is an odd question but maybe someone with a bit more knowledge could help me out!
I strongly suspect that some level of compromised pituitary (and/or hypothalamus) function can and does occur. The Wiki page linked below is a start, a very brief summary of one aspect:
Thank you very much for your reply Rod. I shall have a good read.
I have had below range free ts, or right at the bottom of ranges, and my TSH has never gone above 3.84. I think maybe I will be reading that article, too.
If you have been taking NDT and it made your TSH very low then it will have affected your pituitary leading to low TSH. This happens in treated Graves' patients who have a suppressed TSH for some time. Sometimes the TSH recovers over time but often not fully. The other pituitary hormones are not affected. Was your TSH suppressed while on NDT? What was your thyroid blood results when initially diagnosed?
This paper ncbi.nlm.nih.gov/pubmed/?te... is old but shows the TSH still failing after 7 months. Beware that the T3, T4 figures are (I think) for total and not free values, the free assays hadn't developed yet. Also, note that a lot of studies, including this one, used a TRH stimulation test and there is evidence that TRH "wakes up" the pituitary. Papers I have seen which state hormone levels have returned to 'normal' show in fact that the fT3 and fT4 have returned to the bottom of their reference intervals, not what we would regard as normal (i.e. middle of the interval).
The TSH (and fT3) are less reliable if you are taking T3 containing medications, it's better to look at the fT4 and fT3 around 8 to 12 hours after the last dose.
Thanks jmh111 - Whilst I know the TSH & Ft3 is less reliable when using a NDT -the problem I have is in evidencing it to m GP..... Luckily for me Ft4 & TSH are the main tests they have used -the Ft4 is always in range but my GP worries about my TSH being suppressed ( it always is and has been ever since I have had combined therapy). I have to say I don't have secondary hypothyroidism.
TSH is often normal with secondary/central hypothyroidism. This is why t4 should always be tested.
I was reading this paper yesterday for my mum, who I think has central hypothyroidism as a result of radiotherapy for a brain tumour. Apparently 65% of people who have had brain radiotherapy go on to develop central hypothyroidism but they still haven't checked her t4!
TSH glycosylation is essential for it to attain normal bioactivity, a process that requires the interaction of TRH with its receptor on the thyrotroph.
I am well aware that TSH and its glycosylation is important (and there are several possible ways in which sugar molecules can attach to TSH), but had NOT realised that TRH had a direct impact on it. Hardly a surprise, after all, TRH is a very important part of the whole process. But perhaps it explains why the pituitary part of the mechanism cannot simply adjust its own output according to blood thyroid hormone levels? It has often felt as if the pituitary should be able to act autonomously.
Now, what is the impact of the different glycosylation of TSH... ?
And, of course, very obviously important where the hypothalamus has suffered any form of damage (howsoever caused).
Thanks for that. That part hadn't registered when I read it yesterday. 8 hours in A&E has that effect on ones cognitive abilities. Of course, I may not have registered it anyway
The whole process is definitely more involved than doctors appear to understand.
Your FT4 and FT3 being low suggests that you are not taking a sufficient level of thyroid hormone replacement.
If you are taking the right levels of T3 and T4 medication, your TSH should be low (mine is typically 0.02), because there is no need to stimulate the thyroid into producing more T4.
Hi mum, I don't know if I've posted any of these videos to you by a functional medicine doctor. There are 22 videos regarding low thyroid. I know there are several that bring out the reason for an unnaturally low TSH. This type of medicine attempts to identify some of the root causes behind thyroid dysfunction. It's a little more practical than the scientific explanations you can research. This type of evidence based medicine is far removed from conventional type which hardly look at symptoms. This is #1 if you care to see how he explains it:
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