Always wondered but never asked - I had my thyroid removed years ago due to large goitre(+ blood tests normal so all hypo symptoms in my head said GP). Diagnosed from biopsy with Hashimotos. On T4 only til recently (don't convert well at all). Learned so much from this forum, hence now with private Endo who prescribed T3. So, my TSH is suppressed at 0.02 (used to be 0.01). If I have no thyroid gland to stimulate, what is the big issue with my suppressed TSH? I would just like to be able to understand. Thank you in advance, clever people.
No thyroid gland so where does TSH fit? - Thyroid UK
No thyroid gland so where does TSH fit?
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Lottyplum
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There are two issues with suppressed TSH. Obviously, no thyroid means no effect of TSH there - neither if TSH is high, nor if zero!
First, a suppressed TSH is assumed to mean you are overdosed - and that there is no other possible reason for such a low TSH.
Second, TSH is sometimes claimed to affect things other than the thyroid itself. But if TSH itself affects other parts, then it could be relevant. It is often suggested that TSH has an impact on T4 to T3 conversion. A higher TSH resulting in more/faster conversion.
However, while it is easy enough to see some associations like very low TSH and bone issues, it is much harder to prove a causal link. Say high T3 does cause bone issues, then how do you separate the effect of high T3 versus the effect very low TSH as being the cause? In by far the majority, high T3 and very low TSH would occur together.
Bone and heart are often mentioned because issues with both are often seen in hyperthyroidism (e.g. Graves disease) - at least, until adequately treated.
Similarly with heart issues.
There are also complicating factors like TSH not actually being a single substance. There are multiple slightly different versions. (A bit like wheat flour not being all the same. Some is lower gluten soft flour suited to cake making, other sorts are high gluten and required for bread making.)
Probably the very last thing you want to do is get involved reading about TSH isoforms but, on the off chance you do want to leap at the opportunity, you could start here:
Thyrotropin Isoforms: Implications for Thyrotropin Analysis and Clinical Practice
TSH stimulates thyroidal secretion and has other lesser actions. The hypothalamus and pituitary stimulate the pituitary to secrete TSH and TSH is supressed by thyroid hormones. So, often a very low TSH is the result of too much T3 and / or T4.
If TSH is very low it may be because your fT3 or fT4 (or both) are too high. It could also be because your pituitary is not secreting as much TSH as it should, this isn't always due to pituitary damage, the pituitary can underperform for other reasons. A low TSH is a warning sign, it's an indication to be careful but doesn't always signify your thyroid hormone levels are too high.
jimh111 But what if you have no thyroid, your TSH is suppressed, but your T4 and T3 are not high - maybe 75% in the reference range?
Surely if T4 and T3 are well within range, you're not at risk of developing eg AFib or osteoporosis even if your TSH is suppressed?
I asked 3 well-known endos this question, and they all said it's not the TSH level itself that's the problem, it's the thyroid hormones.
Trouble is, much that has been published is written as if it really is the level of TSH itself that matters. Not that (at best) it is a proxy for FT4 and FT3 levels.
And there is ongoing and unresolved argument about the impact of TSH anywhere but the thyroid itself.
I end up thinking that if the difference between 1 and 5 is dismissed as all being within the reference interval, then why does the very much smaller difference between 0.01 and 0.2 matter? If TSH has any impact outside the thyroid, then what impact does going from 1 to 5 or even to 10 have?
They surely cannot claim that very small differences have a major impact yet much, much larger differences have no impact.
There are individual set points, some people need a little more hormone and some a little less. If we have someone who is perfectly typical they might have TSH 1.5 fT3 5.0 and fT4 16.0 representing mid-interval for each hormone (TSH has a logarithmic interval).
These levels fluctuate in each person to an extent of about half the size of each reference interval academic.oup.com/jcem/artic... , e.g. see academic.oup.com/view-large... .
If fT3 or fT4 falls by about 20% they will probably begin to be hypothyroid, if both were to fall they would be much worse. The same applies if either hormone rises by e.g. 20%, the person will be a little thyrotoxic and much worse if both rise by 20% - even though both hormones are still within their reference intervals. In all these cases TSH would change substantially, most likely moving outside its reference limits.
If one hormone rises e.g 20% and the other fallls 20% there will be little change in TSH. Thus, TSH is an excellent marker for overall thyroid status - IN A HEALTHY PERSON (or at least with an healthy hypothalamic pituitary thyroid axis). Note that levothyroxine monotherapy, or any non-physiologic mix of T3 and T4 messes up this axis.
So, for most people a TSH below the lower limit of its reference interval is a warning sign of danger. The same applies to an equal or greater degree if TSH is above its upper limit but doctors ignore this sign of danger unless TSH is above 10.
Sometimes the axis isn't working properly, not surprising as people visit doctors when they are not well. There can be many reasons but in every case if TSH is not reflecting thyroid status it cannot be relied upon to reflect thyroid status! (stupid statement intended). If TSH isn't reflecting thyroid hormone levels or the clinical picture you cannot use TSH for diagnosis or titrating therapy.
There are cases such as mine where higher hormone levels are needed to achieve a reasonable degree of clinical euthyroidism. In these cases it is likely a low TSH is associated with risk, but unfortunately a normal TSH leads to severe clinical hypothyroidism and much greater risk. You can't always be risk free, the science isn't that advanced.
In summary, a low TSH is always a warning sign of potential harm and shouldn't be ignored. In many cases TSH may not be reflecting thyroid status, people do get ill. In some cases we have to balance the risk of higher than normal hormone levels against the consequences of leaving the patient clinically hypothyroid. TSH is a useful indicator but you have to use it with intelligence.
My story is that on T4 only I needed 200mcg levo daily to stave off hypo symptoms. When new GP surgery reduced levo to 175 I ended up in Surgical Assessment Unit for v severe abdominal pain - like being in labour! Severe constipation+no one would listen! Meds to clean me out for endoscopy stopped the pain! I did everything to address the issue, water, water, water, fybogel+similar but no success. I upped my levo back to 200+all settled down - and yes, my TSH is surpressed but am I to live in pain to please the medics? Now on T3 as well so levo reduced a notch but TSH still suppressed+ has been for years, so what do I do? I live with the risk to be able to enjoy life+pay privately for that benefit!
Lots of us are in this situation. The real answer is for endocrinologists to find out what doses these patients need, why and how to correct the underlying problem. Unfortunately I don't know of any doctor who is attempting this logical approach. In the meantime it's a question of balancing the risks and having a life. We can also do things to mitigate potential problems such as taking exercise (which may not be possible on a lower dose).
I walk every day for about an hour or more - tho been inhibited with chest infection at present - and use our closeness to the seaside to briskly walk along the prom! I used to run every day when younger and wanted to restart even@my age but osteopenia diagnosed made me wary, so for now it's brisk walks+running up+down the stairs! Plan to check about doing some running. Used to love it and ran everywhere -even pushing the pram at speed!! 😎
I walk every day for about an hour or more - tho been inhibited with chest infection at present - and use our closeness to the seaside to briskly walk along the prom! I used to run every day when younger and wanted to restart even@my age but osteopenia diagnosed made me wary, so for now it's brisk walks+running up+down the stairs! Plan to check about doing some running. Used to love it and ran everywhere -even pushing the pram at speed!! 😎
T4/ T3 circulate in the blood. (either from thyroid, or from tablets)
blood passes through Hypothalamus (in brain).
T4/T3 acts on receptors in Hypothalamus.
Cells in the hypothalamus respond to whether levels of T4/T3 are sufficient , too high ,or too low, to satisfy the cells of the hypothalamus.
In response, the Hypothalamus makes TRH (Thyrotropin Releasing Hormone).
When levels of T4/T3 are higher .... Hypothalamus makes less TRH.
When levels of T4/T3 are lower .... Hypothalamus makes more TRH.
TRH goes to the Pituitary (in brain).
Pituitary responds to the amount of TRH by making more/or less TSH ~ Thyroid Stimulating Hormone.
(The pituitary also has some input into how much TSH it makes , because the cells in the pituitary also respond to how high the levels of T4/T3 are, just like the cells in the hypothalamus do).
So , a blood sample measuring TSH allows us to see whether the cells in the Hypothalamus/ Pituitary think they have enough, not enough , or too much T4/T3.
The basic idea behind TSH testing is this ~ if the cells of the hypothalamus / pituitary want more T4/T3 ( high TSH ), then so do the cells in all the rest of the body ...... and if the cells of the hypothalamus/ pituitary have too much T4/T3 (Low TSH) ,then so do the cells in all the rest of the body .
TSH then goes to the Thyroid Gland .... (if there is one).... to stimulate it to make more (or less) T4/T3.
But the process of TRH / TSH production from the hypothalamus / pituitary is the same regardless of whether it ever gets to a thyroid gland or not. (when it does go to a working thyroid, then that thyroid responds by making more , or less T4/T3)
TSH is therefore a 'proxy' measure of the levels of T4/T3 in the blood ,(measured via the effect of T4/T3 on cells in the hypothalamus / pituitary).
Doctors have been taught that this is a reliable method of knowing whether all the other cells in the body have enough, or too much ,T4/T3. ( ie. if TSH is lower than range, it's assumed all the cells in the body are getting too much T4/T3 ... hence all the fuss about Low TSH from GP's )
The reason that we can't rely just on TSH once we are taking oral thyroid hormones is very complicated and i haven't got the brain to explain it simply this morning ...... but the science / research explaining it are in this post (there is also some info on how taking T3 lowers TSH more than T4 does): healthunlocked.com/thyroidu.... tsh-is-just-the-opinion-of-your-pituitary-about-your-dose-but-your-pituitarys-opinion-is-a-bit-warped-once-you-take-thyroid-hormone.
I have tried to explain it simply in this post : healthunlocked.com/thyroidu... explanation-of-what-*high-tsh-is-telling-us-when-our-ft4-level-is-normal-on-levothyroxine-the-shoe-size-analogy.-
on levo we end up with "higher T4: lower T3" than a normally working thyroid would give us ... and this changes the very fine tuning of the H/P/T axis (hormone regulating system).... so on levo , the T4 is a bit higher, the fT3 is a bit lower, and the TSH is "shifted" a little bit lower. than it would be if T4 and T3 are both coming from a thyroid gland.
there is evidence that on levo only (due to having lower T3) not all body tissues are getting enough T3 ,even though the pituitary is satisfied that it is getting enough T4/T3 ...ie. the cells of the heart, or skin, or muscles, or gut ,etc ,may not be.
very over simplified explanation is ~ there is a mechanism making sure the pituitary/ hypothalamus gets served T3 'preferentially'.
But Doctor training hasn't explained that to them yet .. so whenever Doctors see a below range TSH they will worry that the it means the whole body has too much thyroid hormone.... they don't know that once a patient is on Levo (with higher T4: lower T3 : lower TSH) it doesn't always necessarily mean that .
Thankyou for this. More reading for me. Another question! I had my thyroid removed in 1981 and after being put on 200 levo, never had a blood test for years! Then I only had an annual thyroid blood test, told all ok+on I went. Only in the last 5 yrs told my TSH suppressed+had been suppressed for 10 yrs or more (moved house+new GP surgery). So, if TSH is such a big issue for GPs how come only recently do I get panicked GPs telling me I'm over medicated, reduce my levo+cause all hell to break loose in my body? (The major reason I sought refuse from private Endo!) I'm just trying to unpack the what and why I'm ok for over 30+ years and then, no no no, you're over medicated!!
Simply because different GP's will have different opinions about low TSH.... some know more/ have more experience than others .
some will worry about at a very slightly below range TSH ,even if patient is well and T4 is well within range.
some won't worry about it as long patient is well and is not showing any symptoms of overmedication and as long as fT4 is not stupidly high .
some won't worry about it as long as it's measurable eg 0.04 upwards , and will only be concerned if it's totally supressed (too low to measure) ie<0.001.
some GP's are better at looking at the individual patient and their history , and had more time to wonder what may be happening in an individual and wonder why their results don't always fit the box .....but some are led more by tick box systems... and increasingly so as the older more experienced GP's are leaving in droves.... the newer lot are working off algorithms for everything ... "computer says TSH is too low"
also ,don't know if this is you , but ~ when thyroid is removed due to cancer then TSH is kept deliberately low and will be kept low for several yrs to discourage any regrowth of cancer cells (because TSH stimulates thyroid cell activity .. and they don't want to stimulate activity in any tiny remaining pieces of thyroid , in case it has cancer cells lurking in it) .
Older policy was to keep the TSH supressed for a very long time/ forever in thyroid cancer patients following thyroidectomy .. but nowadays they have decided it doesn't need to be kept low for so long in all cases ... if yours was removed due to cancer this may be another reason why they weren't worried about your low TSH previously .
My thyroid was removed due to large goitre that was impacting my breathing - no cancer but Hashimotos. Mind you it took about 4 yrs to get action+only cos my husband insisted on a 2nd opinion. There was no Dr Google then, no access to research (other than the library) but I was a mum with a young child+ just glad to get an answer to all the awful symptoms, which of course were hypo symptoms - but even then, my blood work said I was within normal range so it's all in your head scenario, which was the last straw. Personally I believe I had started with Hashi before or whilst pregnant - gained so much weight, protein in my urine, high BP followed by pre eclampsia+emergency c section. From what I've read, all could be connected to under active thyroid. With my 2nd child, was on levo, went private, gynaecologist had my thyroid levels checked@every visit+scans to check development. No pre eclampsia, normal delivery+worth doing without other things for peace of mind+healthy mother+baby!! I think more so now that I'm prepared to do without things to have an Endo that recognises my quality of life is more important than numbers!
This last explanation of your thyroid journey totally highlights the stupidity of blindly following the guidelines - and shows that there is a lack of understanding on how to interpret the TSH, in relationship to the Free T3 and Free T4 results and ranges.
Trouble is in many primary care surgeries the doctor can only action a TSH reading to dose and monitor on alongside an occasional T4 - so becomes totally reliant on the lab and a computer dictating and flagging up what further action is required - and I'm not aware the computer knows your medical history.
I'm guessing your previous doctor had some understanding and used the guidelines as just that - a guide - for when and if, medical knowledge of the patient is lacking.
My previous GP was super! I could talk to him, have a laugh with him. If another GP picked up my annual bloods+I got a call to reduce my levo, I got an appt with my lovely named GP + he knew I would be there challenging the decision. He would laugh cos he expected me+there would be no change in levo! He knew I only functioned if T4 near top of range. Mind you, I didn't know then that I was a poor converter of T4 - T3. I have learned so much from this forum. I would still be fighting the perceived TSH wisdom @the new surgery and there's only so much fighting you can do when overwhelmed with hypo symptoms+pain. I am just so v grateful. If GPs+even Endos only realised their ignorance causes such horrific consequences to our health maybe they'd take a step back at look@us holistically rather than just body parts! Btw, my GP app contained a new 'Frailty chart' (I'm nearly 75) and anyone under 0.2 is classed as fit! That's me! I think that's because of taking over my health rather than it being in GPs hands and doing everything they say!!! Same for my husband - off blood pressure meds (unbeknown to surgery) and using olive leaf extract+beetroot extract instead. After his latest GP MOT was told to keep doing what he was doing as it's working! They'd never heard of olive leaf or beetroot extract for high BP!That's what a bit of research will do!! We are the new 60s!!😁
I would just add that the pituitary doesn't know your thyroid has been removed. It reacts to thyroid hormones in the blood whether they come from your thyroid or from a pill. So, the TSH is not going to disappear when you have a thyroidectomy. The pituitary is going to continue to produce it whenever it considers thyroid hormone levels are low, and stop making it when it is satisfied there is enough. The pituitary doesn't always get it right, but it continues doing its thing regardless. 
Thankyou. That makes sense! Esp the part about 'the pituitary doesn't always get it right'. If only GPs realised that! As I said to an NHS Endo (who I believe was not a thyroid specialist) as I held up my thumb, "my thumb print means I am unique as no one else has my thumb print and the rest of me is unique, meaning 'one size fits all' does not work!" She discharged me after my first appointment!😁
Ah, she couldn't tolerate the truth, could she! They don't like individualists! No, I don't suppose she was a thyroid specialist. There are very few of those around - even when they claim to be.
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