Thyroid UK
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Help - do i need a higher dose of thyroxine?

I have currently been poorly on & off for the last 6 weeks with water infections, throat infections, lack of energy etc. I asked the GP if it could be my thyroid & she said no (i currently take 100mg of thyroxine). Finally she agreed to do blood test which showed my level has dropped from 18 to 12 (norm being between 12 -22) but she still wants to wait another 6 weeks. Surely a higher dose would have me feeling better as I'm not sure how much longer i can go on feeling this crap!

12 Replies

If your not happy with your Dr's advice ask to see an endocrinologist. I dont think anyone on here is qualified to give advice on how much Thyroxine you need. It seems to me reading these comments and in my own experience that half the Dr's aren't qualified enough in Endocrinology to be able to judge, I think if they have a straightforward case of over or under they can cope anything that deviates from that and your best to see a specialist and ask for further tests. I do sympathise with you feeling ill all the time ive spent most of the week end in tears myself. It gets to you.... good luck. :)


Hi, The big question here is why your level has dropped so dramatically. What is the approximate timing between the test that showed your level to be at 18 and the most recent one where it was 12? Also, is that the number for the TSH level or for the T4 level?

Has anything changed with respect to what, when and how you take your thyroxine? e.g. Has your pharmacy given you a different brand of thyroxine to the usual one they supply? Do you take any other medications at the same time as your thyroxine (even vitamin pills)? Do you eat or drink anything around the same time as taking your thyroxine?


12-22 sounds like it's t4.

Interestingly I've seen this range come up more and more while my t4 of 11.4 was not flagged. Does anyone know whether different laboratories give substantially different readings or whether their reference ranges vary mainly because of different statistics?

RedApple makes a good point - why has your level changed so much? This probably warrants investigation.


My local lab has a T4 range of 9.01 - 19.05. Ranges do vary, which is why it's very important to get the reference range for the specific lab that does your test. The range that the lab uses is generally quoted alongside the test result when the lab sends it to your surgery. Anything outside the range is also usually flagged as either low or high by the lab.


Thanks. Do you know why reference ranges vary?

I don't have it on my printout, but I saw it on the dr's computer screen - I think it was 10 something.


I believe in most cases it's basically down to the fact that the testing kits are supplied by different manufacturers, and the ranges are provided by the manufacturers for their specific kit.

The history of how the so called 'normal' ranges were originally arrived at is more complicated. I would provide a link for you to read up on it, but I can't recall where it is at the moment!


(Sorry for hijacking this thread, but this is relevant)

This is what I found on wikipedia:

"References range may vary with age, sex, race, diet, use of prescribed or herbal drugs and stress. Standard reference ranges should theoretically not vary with the instruments and lab techniques used, but practically it may do so when inaccurate methods are used in establishing standard reference ranges. Also, the samples may deviate from normal distribution. Furthermore, reference ranges only denote what are usual values in the population, and do not directly correlate with the ranges for optimal health. In case of substantial difference, there may additionally be an optimal range specified for the substance. Finally, the test procedure itself may be erroneous or inaccurate."

So in theory the difference in the ranges should just be because of different statistics. I wonder if the laboratories have a way of ensuring good samples... otherwise if they only take from an area that's prone to (for example) hypothyroidism, their range would be skewed.

I'm starting to agree with those that recommend treating mainly according to symptoms and using blood tests as a guide.


Thanks (looks like we posted within moments of each other).

If you do find it please let me know - I would be interested to read it.


If you want to spend the rest of the week trying to understand thyroid testing, have a go here:

Especially "4. Serum TSH (Thyroid Stimulating Hormone/Thyrotropin) Assays"

Treating by symptom has a lot to commend it. But it can be problematic, especially in less experienced people (e.g. those more recently diagnosed), as so many symptoms can occur both under- and over-treated people. Clearly backup by some form of testing is highly desirable.

All the best



Thank you for the link.


Thank you for all your advice - I've been to see a different dr today who took one look at my levels and said they were way to low and has up'd my thyroxine tablets. My TSH level was 7 x higher than it should be & T4 level is dropping. Why the previous Dr I saw couldn't see that is beyond me! Thanks again.


Brilliant - hope it does the trick!


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