FT4: (1) What are the long term implications o... - Thyroid UK

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FT4: (1) What are the long term implications of 'low in range'? (2) Will decreasing T4 affect FT4? (3) How does T3 impact on FT4?


20/12: TSH 21.2 (0.35-5.5), FT4 13.3 (10.0-22.7). Retesting inc T3 30/12. 100mcg T4.

1) GP is keen to raise my FT4 as "there are long term health implications when FT4 is low in range". I was sulking, having been told CCG won't permit T3, and snapped there wouldn't be a long term future for me if my problems with T4 aren't sorted. Any ideas what he meant?

2). He mentioned possibility of reducing my T4 after retesting tomorrow as I'm complaining about so many side effects. What effect is this likely to have on FT4?

3. How does T3 solus or in combination affect T4?

13 Replies

1) I am sure I am stating the obvious when I say that T4 is not an active hormone. You can have normal or above range T4 and still be hypothyroid. T4 converts to T3 so your GP should test FT3 as well.

In any case you are underreplaced and should increase your thyroxine. If you have normal conversion of T4 into T3 your T3 will go up as well. If you still feel hypo I suggest you start taking T3 as well.( I can PM you with where to get it if you needit.) You will have to wait another 6 weeks to retest unfortunately.

2)Sorry I dont know what your side effects are but I think that sometimes it is the hypothyroidism rather than side effects from thyroxine that give the symptoms. I was under replaced for many years but I was never constipated but very much the opposite, but it was not side effects fron thyroxine. It can be hard to differentiate. What ever you do do not reduce thyroxine.

3)If you take T3 by itself or in combination your T4 will be lower, and your TSH very low or suppressed. Measuring your TSH and T4 will then be pretty useless because it would tell you very little.

There is a possibility that T4 has its own function in the body other than being a prehormone, which has not yet been found out, and the same for TSH, I have read somewhere that you need T4 for hair growth for example. It is all very complex and most Gps are deffinately not the people to ask. I think most people do best to have some T4 in their thyroid replacemet but there are people here on this site that has such severe T4 resistance that they convert very little and need T3 only. Within the whole thyroid community, I think that that is quite unusual. But if you have little or no functioning thyroid I beleive you always need some T3.

Hope my answer is not too confusing, I have a rotten virus and a temperature today. And I have to drag myself to work


Clutter in reply to roslin

Thanks Roslin. I hope you're feeling better today. Your answer is quite clear, thank you. I stopped all thyroid meds for 4 weeks in Nov, having stopped T4 back in Sept. I really felt so much better with all the distressing side effects stopping. I was 95% bed bound & couldn't figure out any other way to see if the symptoms were due to being surgically hypo or T 4.

Resumed 100mcg T4 Dec 7 and TSH is down from 107.5 and FT4 up from 4. Unfortunately, side effects are also returning & I can't permit myself to become so unwell so shall add T3 with a view to trialling NDT if I continue to feel unwell.

I'm not sure how much difference 10 days to retest will make but I'll do as requested.

Is there a typo here? You say your TSH is 21.2 and yet your GP is considering reducing your T4? He should be increasing it. Whatever is he thinking? It is clearly outside the reference range and your free T4 is also too low. For the moment do not worry about your CCG not allowing T3. Just concentrate on the very high TSH and low free T4. The T3 may sort itself out if the rest is right. Suggest you post the new blood results with ranges but do not accept a reduction in your T4, unless it has gone from low to over the range in ten days, which seems highly unlikely. Maybe a good idea to look around for a new doctor?? Do hope you get proper help soon. x. Ps To answer your question about T3, it has a marked lowering effect on TSH and is usually given with a reduction in T4, so this result would also be low. Your body converts T4 to T3, or should do, which is why I suggest you wait a while to get the T4 right, before worrying about whether you need T3.

Clutter in reply to Hennerton

Hi Hennerton,

No typo. GP isn't talking about reducing T4 until/if TSH and FT4 are in range. He has requested FT3 on latest test. Trying to help me but his hands are tied vis a vis T3. I've become more & more unwell since completion thyroidectomy and starting T4 in May 2012 and reducing T4 from 200mcg to 100mcg over the period. Prior to RAI, I was ok on T3.

Prior to stopping meds TSH was suppressed 0.03, FT4 17.1 (9-19) and FT3 3.1 (3.2-6.2). Endo was content for FT3 to be below range & said stay on 100mcg T4. I simply couldn't face a further 6 months feeling so ill and started self medicating, detox etc to discover I can feel better and will need ti find the right meds/ combos.

Thanks for replying.


These are two an extracts and go to the link to read the whole article.:-

We at Thyroid UK believe that you need to know your Free T3 level too because this will often show low if you are not converting, and high if you have blocked receptor cells. Even if you are converting, the body needs the extra T3 that a normal thyroid produces. There has been some research to show that people feel better on a mixture of Thyroxine (T4) and Triiodothyronine (T3). Effects of Thyroxine as Compared with Thyroxine plus Triiodothyronine in patients with hypothyroidism – The New England Journal of Medicine Feb.11, 99 Vol. 340


Taken from Medicine International 1993

"The aim of thyroxine replacement therapy is to normalise plasma TSH and to achieve a clinically euthyroid state. To obtain this, FT4 and TT4 have to be maintained at, or just above, the upper reference interval".

On this link go to the date April 22, 2007 to read the question/answer.


T4 is a prohormone as Roslin said, it is supposed to convert to enough T3 which is the active one we need in our cells in order to function. If on levo alone, we also have to have enough of it to convert to sufficient T3 for our needs. Many take T3 alone.

You say your GP wont add T3, but Dr Toft in his article says that some do need the addition of some T3 to a reduced T4.

Glynisrose in reply to shaws

It always amazes me that anyone could think that if the thyroid makes T1, T2, T3 and T4, why they can replace that with T4 alone!!

shawsAdministrator in reply to Glynisrose

You are correct. It is due to big pharma wanting profits, the prescribers want the cheapest and have believed the promotional studies. Account is not taken of (what patients desire) and the other side of the coin when patients have to have other meds to control continuing or new symptoms which are diagnosed as 'not thyroid', i.e. heart, blood pressure, muscle and joint pain, diabetes, etc etc.

Dr Peatfield says that" T2 alone is effective in liver metabolism, and also that of heart , muscle tissue and brown adipose tissue.... It is as good or even better than T3 in lipid (fat) metabolism.

T2 is not given by any doctor in the UK but is part of NDT which is probably why they work so much better than T3 or T4 on their own. T2 can also breakdown body fat without breaking down muscle tissue as well"

Clutter in reply to shaws

Goes to look up adipose :) I don't think I have any body fat left after 20+ months of T4. Muscle gone too :( Look like a skeleton with skin drawn over innards.

shawsAdministrator in reply to Clutter

Clutter, you made me laugh. A lot of people would be envious of you.

Clutter in reply to shaws

Grass is always greener... I suspect that weight gain prior to weight crash may have been Hashi's wicked teasing ie I can give you cleavage and shapeliness... and I can just as easily take it away again. Ppfft!

Clutter in reply to Glynisrose

I don't think they care. Pharma benefit by selling more drugs to offset side effects and co-morbidities, so that's allright :( I rarely saw a GP prior to ThyCa. Now I haunt the place. Surely a CBA of GP time v cost of T3 or NDT, when appropriate, ought to be studied.

Clutter in reply to shaws

In July my FT3 was below range 3.1 (3.2-6.2). Endo wasn't concerned despite co-morbidities piling on. ECGs showed some minor arrhythmia/abnormality, and x-ray showed expanded lungs. COPD was considered & spirometry recommended.

By the time I had the lung function tests I'd been off T4 three months and was breathing easily. The results looked good and when the official interpretation comes through I'll be gobsmacked if COPD is confirmed, especially having been told my lung age is 3 years younger than my chronological age.

Thanks for the link, I shall have a good read after I've eaten.

waveylines in reply to Clutter

So sorry to hear that you are having such a rough time. Your GP is right in the sense that you clearly need thyroid meds according to your blood test results. The key to this is that is sounds like you are intolerant of, i am assuming levothyroxine? The reason why your GP is looking at reducing your meds is to see if it is more slowly re-introduced that you will be able to tolerate it better. This does happen to some people. How long have you been on Levo?

You GP will be worrying about what can happen to you if he doesn't treat your hypothyroidism -e.g.high blood pressure, heart problems, dementia like symptoms etc....so this is probably why he snapped -would have been good though if he had instead taken the time to talk things through with you. instead...lol!!!! Your endo should know full well that if your are not responding well to levo and your T3 remains low that he should according to NICE guidelines be prepare d to look at T3 or a combination medication. Dr Tofts book can be a useful one for this to quote from....

Have you tried a NDT?

The GP will have their hands tied by the endo.....though I have to say that in my experience GP's do not have to implement the recommendations of a specialist -mine have certainly ignored them in the past!!!! (when higher costs were implicated...lol!) Have you thought abut asking for a second opinion but before you do so make sure you find a good endo first before asking for the referral?

In the meantime I suppose you could consider privately purchasing NDT but it would lead you into self medication -this is not to be recommended of course - but some of us have been forced down that route to get well.

I think if it was me I would contact Lynn for the names of the good docs on her list..... amd check 'em out. Hugs x

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