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Thyroid UK
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Thyroid levels confusion

Hi I'm new to this site.

I have had under active thyroid since 2001 when it was first confirmed as borderline

i was advised to have thyroid function test again in 6/12 months, but when i moved away it took years to persuade a GP to carry out a thyroid function test

when i eventually succeeded i achieving this in 2006 i was prescribed 25mg thyroxine and basically forgotten about for another 2 years, after which the dose was increased to 50mg and later still to 75mg and over the last 3 years to 100mg

while waiting to get to the 100mg per day, my weight increased, i developed high blood pressure and high cholesterol levels, so, because my borderline under active thyroid was neglected for up on 12 years i was left to develop a string of hypothyroid induced other health conditions, i have not felt healthy since a bad infection in 2001

and i was a very health conscience person and fit.

Recently i had my thyroid function levels tested by a private health screening company who came up with the results which read my T4 levels were raised to 24.1

when for last few years NHS test was 8.80.-21.00pm0l/L

I now don't know who to believe, does anyone know what marker does the NHS use to determine the correct levels for under active thyroid? i would be grateful for some advice, thank you

11 Replies

Maggimai Your story is, unfortunately, so familiar. These doctors are letting so many people down with dreadful consequences as you know.

Do you have all the results of this private test? Can you post them all with reference ranges please.

The older NHS results with ranges would be good too if you have the last one for comparison.

The NHS ranges will most likely differ from the ranges the private lab uses. It doesn't matter at all, it's where in the range you fall (as a percentage) not what the actual number is.

For example, my most recent test done privately showed FT3 at 5.15 (range 3.1-6.8) so I was approximately 55% through the range. A NHS test done a couple of years ago showed my FT3 as 5.5 (range 2.1-6.0) so I was 87% through that range. There is a reason for the big difference, but that's just to show you how the ranges differ.


Hi Seaside Susie, thank you for responding

This is what really confuses me, i don't seem to have a T3 reading as you state you have, let me give you what i have here;

2001--- Ireland--Borderline low reading TSH 6.74 mu/l*

Free thyroxine 14.50 pmol/l

(no mention of T3 )

2013 June NHS - thyroid function test-(MEH)- Norman-No acvtion

Serum 3.34 mu/l (0.30

TSH level ---


Serum 15.0 pmol/l (8.88

free T4 level 21.0)

2015 Sept NHS thyroid function test (jfb)- normal. no action

serum TSH level 0.48 mu/l 0.30- 5.00mu/L

serum free T4 level 17.2 pmol/L 8.80- 21.00pmol/L

2016 June( Private test) TSH 0.30 mIU/L (standard range) 0.27- 4.2

FT4 24.1 pmol/L (standard range) 12.-22.0

This is all i got to date. i hope you can make something of them, the private test gives their standard range, i have no idea what range the NHS uses, also when i had that private test i had not taken my thyroxine dose that morning, i had fasted and did not have blood taken till 2pm.

thank you for any advice you can give and for all that you have given

hope to hear from you soon.

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OK Maggimai This is the easiest way of understanding what you have given, ranges are in brackets after the test result:


TSH: 6.74

FT4: 14.5


TSH: 3.34 (0.3-5.0)

FT4: 15 (8.88-21.0)


TSH: 0.48 (0.3-5.0)

FT4: 17.2 (8.88-21.0)


TSH: 0.3 (0.27-4.2)

FT4: 24.1 (12-22)

Am I right in thinking

1) You were on 100mcg thyroxine for both the 2015 and 2016 tests?

2) The 2016 test was done by Blue Horizon as those are their ranges?

3) Did you take your thyroxine before both the tests?

4) What time of day were the tests done?

In 2015 your FT4 was 68% through the range.

In 2016 your FT4 was 121% of range.

Your 2016 results show that you could be over medicated although your TSH is still in range.

How do you feel?

When you had your private test done, did it not include FT3? This is important, especially when you have a high FT4 and a low TSH. Mine was like this and my GP keeps saying I am over medicated. However, my FT3 was only half way through the range so it showed I was not converting T4 to T3 and I had to do something about that.

What you really need, if you haven't already got them is:




Thyroid Peroxidase Antibodies

Thyroglobulin Antibodies

All these are included in a Blue Horizon test bundle and the antibody tets will tell whether you have autoimmune thyroid disease or not.

And as Greygoose has mentioned,


Vit D



are all important and can be done as part of the Blue Horizon Thyroid Plus Eleven test.

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Hi Seaside Susie, i have now got print out of most recent Thyroid function test, the results have been included with other tests on the paper, however this time it gives a T3 reading (which was stated as Normal)

5 pmol/L 3.10-6.80pmol/L

T4 level 23.4 pmol/L 10.30-24.50pmol/L

TSH level 0.2 miu/L 0.40-5.50miu/L

This result puts my T4 level too high according to the GP and suggested another test in October, can you give me any advice as to what exactly is the T3 function got on the thyroid. any info at all would be gratefully accepted

Thank you


Maggimai T4 is the storage hormone and this has to be converted to T3 which is the active hormone which is needed by every cell in our bodies, see thyroiduk.org.uk/tuk/about_...

When we take Levothyroxine only, it should convert to enough T3 for our needs. If it doesn't convert well enough we may need to add synthetic T3 or to change to Natural Dessicated Thyroid (made from pigs thyroid and contains both T4 and T3). Synthetic T3 and NDT are very difficult to get on the NHS.

Your FT4 is not too high, it is still within the reference range. Your TSH is slightly below the reference range but that's of no real significance. Basically, TSH is a pituitary hormone not a thyroid hormone, and taking Levo means that your pituitary gland is getting the message that you have enough T4 so it doesn't produce much Thyroid Stimulating Hormone (TSH) which is what tells the thyroid to produce T4.

You are managing to convert T4 to T3 as your FT3 is 5 (3.1-6.8) but your conversion isn't quite good enough. For good conversion the FT4:FT3 ratio should be 4:1 or less and yours is 4.68 : 1. Your FT3 should be around 5.9.

You are not over medicated, your FT3 would be over range if you were over medicated.

If you get those vitamins and minerals mentioned above tested and they show deficiencies then that makes a difference to how your thyroid hormone works. All Vits and mins need to be optimal for thyroid hormone to work properly so it really is best to get them checked, privately if necessary.

Just wanted to mention that if you reply to a member's post directly under their message (by using the Reply button in the message box), it sends them a notification so they know you've replied. Or you can send them an alert by putting @ in front of their name (no space). Either way your post won't be missed :)


Hi Seaside Susie, thank you for your reply, sorry for not responding earlier, i don't have a computer in my home; i have learned much from your information and i am going to ask my GP for those vitamin/mineral tests, also the Thyroid Peroxidase Antibodies/ thyroglobulin Antibodies tests, i also noticed an added few more words at the bottom of the test results lab printout, it reads; Biochemical Test; noted patient on thyroxine 100mcg, TSH suggests under replaced.

Would you have any idea what effect this footnote has on the the overall thyroid function test?

any information you can pass on would be gratefully appreciated thanks again.margaretnesbeth


Hi Margaret

I am amazed! Did it really say

Biochemical Test; noted patient on thyroxine 100mcg, TSH suggests under replaced.

If that is on the lab report where your results were

5 pmol/L 3.10-6.80pmol/L

T4 level 23.4 pmol/L 10.30-24.50pmol/L

TSH level 0.2 miu/L 0.40-5.50miu/L

then with a below range TSH I would have expected it to say over replaced. But, the lab has given it's opinion to your doctor so I can't see why your doctor is ignoring it. They say 100mcg isn't enough thyroxine (I'm still amazed!)

How do you feel? Do you want to try an increase in thyroxine? If your GP isn't keen you could suggest maybe a 12.5mcg increase rather than a 25mcg increase, reminding him of what the lab report says.

Or you could wait until you get the results of the vitamin and mineral tests and see what they're like.


Hi Seaside Susie, thank you for your response 4 days ago, yes, i found the Biochemical Test comment odd in fact i found the manner in which the blood test was laid out in the surgery A4 size page odd, as the results of blood test for Thyroid readings and Glucose and liver function test all over the place, the page also included the results of a chest xray i had around the same time, for example on one line you get the T4 results the next line is part results of the LFT, next line is the xray results, in fact chest xray results only state the lungs are clear, it makes no mention of the troublesome extra cervical ribs i have in the lower neck which joins to the shoulder joints, no mention of the botched surgery carried out in 1987, which makes me query the correctness of any of those results.

when i contacted surgery to ask if the results of those tests had arrived back from the lab yet, i was told" some have returned " she went on to state the various tests done were all sent to surgery at different times, i got the impression whoever was doing the glucose test sent on the results to the surgery when done and so on and so on. i got the impression whoever had the job of compiling those various results from the lab simply typed them into computer any which way, with this sort of lax treatment of my results when writing them up, one got the impression they would not be presented to a GP in that higgly piggly form, to me it shows a lack of interest in me as a thyroid sufferer, i noticed there was absolutely no interest in the results on the private LFT, the attitude was one of " so, you have a fatty liver, so what!!!" go on statins!!. what would your comment be on this sort of attitude.

Oh, and of course my thyroid problem, i learned through accessing my medical records, was due to depression etc etc, i was livid when i read that about myself as i have no history of treatment of depression or of complaining of depression to any one in NHS. as far as i'm concerned it is purely stated on the grounds i am divorced and have been a single parent ect, it is pure bias against women in my situation. it would never be thought of my former husband.

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I'm not sure what you mean by 'marker'. Every lab has it's own ranges, so you have to judge your results by those. Why not post all your results - you surely have an FT3 done, no? - and let us see the results with the corresponding ranges. Then people will be able to make intelligent comments. :)

I'm afraid doctors know very, very little about thyroid. Yes, you were badly treated, but whatever health problems that has caused will probably resolve when you are optimally treated. Cholesterol (not a problem, anyway) will go down and weight will come off, etc.

You should have been started on 50 mcg levo - 25 is too low and can cause more problems than it solves - and tested six weeks after. If doctors don't know that - which a lot don't - we have to know it, and make sure we get the right treatment. And, if your TSH is above 1, and your FT4 isn't up near the top of the range, ask for another 25 mcg increase, and then test 6 weeks after that. And, you continue like that until all your symptoms have gone.

How long have you been on the 100 mcg dose? Just make sure you go back six weeks after starting it and have a test. Arrange the test for early morning, and fast - just drink water. And leave 24 hours between your last dose of levo and the test. And, no, your doctor didn't tell you any of that because he doesn't know - he has no idea!

Also, when you go back for your test, ask to have the vit D, vit B12, folate and ferritin tested. If these aren't optimal, they will exacerbate your symptoms, and make it difficult for you body to use the hormone you are giving it. Optimal for B12 is 1000, and the rest should be at least mid-range - and doctors don't know about that, either. So, it's down to you to get them optimised yourself, I'm afraid, like so many of us are doing. It's a dire situation, but that's the way it is. :(

Oh, and, and, if your antibodies haven't already been tested, it would be a good idea to get them tested, too.


Thank you so much Greygoose, i will take your advice, i have been mucked about by GP' i felt knew no more than i did about my condition.

i will try to give you my test results readings soon, i have just begun asking for print outs of my tests results, another thing that bothered me was the discovery on the NHS blood test forms it was printed that i was not on thyroxine meaning i was not prescribed treatment for under active thyroid, i don't know how long this was going on, possibly from the start, this could mean after the first diagnosis for hypothyroidism the subsequent blood tests forms stated i was not prescribed thyroxine, surely this would have an effect on the true state of my thyroid function test, as i have always taken my thyroxine tablet an hour or two before the blood test, have you got any opinions on this? please let me know, thanks a million.


Well, taking your thyroxine tablet an hour or two before the test, means that all you are measuring is the dose you just took. It will give you a false FT4 level, and would explain why your FT4 was so high. But, it probably won't touch the TSH, because that reacts more slowly. So, anyway, I wouldn't do that anymore, if I were you! What affects the TSH is time of day, and eating. It is highest early in the morning, but lower if you have breakfast first.

But I don't think it makes much difference to the results that the form stated that you weren't on any treatment. It's just sloppy, that's all. You'd think they could at least get that right!

Do you not have the results of your private test to hand?

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