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Thyroid UK
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Blood Test Result and letter from doctor !!

Serum TSH level <0.01 mu/L (o.27 - 4.2) "abnormal"

Will be filed as :0.01 mU/L


If patient on T4 suppressed TSH suggests dose may be to high. Usuan target for treatment is to bring the TSH within the reference range unless treatment for thyroid CA when TSH suppression is desirable. (UK Thyroid guidelines 2005)

Serum free T4 level 21.5 pmol/L (12.00 -22.0)

Serum free T3 level 3.3 pmol/L (3.9 -6.8) Abnormal

Thyroxine being reduced fron 150 mcg to 100 mcg.

Can anyone explain this to me in something I can understand.

Many thanks


5 Replies

Hi. It does seem very confusing doesn't it! The important thing is how you feel. If you feel well on this dose, and not at all over medicated, then I don't think the dose should be changed. If you don't feel well, this needs to be investigated. Reducing your dose isn't necessarily the way forward.

TSH is the hormone that tells your thyroid to produce more thyroid hormones like T4 and T3. If it is too low in a healthy person it suggests that they have too much thyroid hormone in their system. Unfortunately this is often believed by doctors to be true for people on thyroxine.

T4 is a thyroid pre-hormone. It is what the thyroid produces most of. It needs to be converted to T3 (the active thyroid hormone) before it can be used in the cells. Sometimes conversion doesn't work very well so people can have a really good amount of T4 in their system but too little T3. T4 is thyroxine, similar to what you are taking.

It appears from your results that, although you have a good level of T4, your T3 is low. There can be various reasons for this but it suggests that you actually need to be taking liothyronine instead of thyroxine. Liothyronine is T3, the active form of the thyroid hormone. It would be worth asking if you can get this prescribed instead of levothyroxine given that your T3 is low.

Bear in mind that it is not uncommon for TSH to be suppressed if you are taking thyroid hormones such as thyroxine. It doesn't necessarily mean that you are over medicated and shouldn't be read as such without carefully considering T4 and T3 levels.

I hope this helps a little. You might also find the main Thyroid UK website helpful.


Carolyn x


Thank you that was very helpful. x


These results with FT4 at top of the range, but FT3 below its range, suggest that the levothyroxine is not being converted into the active T3. The GP who reduced the levothyroxine by 50mcg, a reduction of one third of the 150mcg, does not know what he is doing. He or she is oblivious to the FT3 being below its range, but thinks that the TSH figure indicates hyperthyroidism or overmedication. Action should not be on the basis of the TSH, but stem from the FT3 being below its range.

You are entitled to seek early referral to an endocrinologist who can investigate the reason for these results, not simply because your GP does not know what he is doing which is evident, but because these results indicate possible conditions requiring specialised investigation and treatment which only a more highly qualified and skilled specialist can undertake and, if appropriate, prescribe for.


I agree with the previous answers. I would like to add that I had exactly the same experience, the doctor reduced my thyroxine from 150 to 100. That is a disastrous drop! On the main Thyroid UK page, is my story of what happened when my doctor did exactly the same as your doctor wants to do:


When you get to the page, go to the bottom and click on 'Marie's story'.

These accounts are not just to shock but to inform. Mine is a 'success story' but the journey to success was very frightening and long. Please do read it. I would like to stop it happening to someone else.

Marie XXX


Thank you for that..........I to have had strokes but never thought it could be anything to do with my medication


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