TSH & FT4 readings on T3 only - help! - Thyroid UK

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TSH & FT4 readings on T3 only - help!


Good morning. I haven't posted recently but I would be very grateful for some advice as I have been called in to see my GP tomorrow. I take 20mg (10mg at night,10 in the morning) NHS Liothyronine daily. I had a routine TSH/FT4 blood test done so didn't take my T3 in morning as originally instructed by my endo 9 years ago. The results came back TSH: 4.52 (0.27 - 4.20), FT4: 5.7 (12 - 22). The surgery asked for a repeat test. By mistake I took the morning dose (about 2.5 hours before) but figured it would lower the TSH test result which would be a positive thing and make them less likely to stop prescribing T3 - which I am so worried will happen. However, the result came back TSH: 6.71/FT4: 3.5 which isn't what I was expecting! What do I say to my GP? If I admit that I took the morning dose is this likely to make him think I shouldn't be on T3. As it is, I would have thought the interpretation is (of the first and more accurate test) I should be on a higher dose of T3 (some chance!). So my questions are: should I tell my GP about the morning dose for the second test ? And why did I get a higher rather than lower TSH reading (and lower rather than higher reading for FT4) for the second test? Or am I going mad and this is what would be expected? Thank you for any advice.

9 Replies

Were the two tests done at the same time of day and fasting? TSH is highest early in the morning and drops throughout the day. The FT4 is irrelevant.

I wouldn't bother to tell your doctor about taking the dose before the test, they don't believe it makes any difference - and it wouldn't make any difference to your TSH or FT4. The TSH doesn't react that quickly. However, it would have made a difference to the FT3, had they tested it.

Either way, that TSH says you need an increase in dose. Your FT3 is probably very low.

Thank you Grey Goose. The tests were done at the same times (approx. 9am) but I hadn't fasted. The last FT3 test I had was September 2016 when it was 4.6 (3.1 - 6.8). However, I didn't realise they were going to test it so had taken the last 10mg dose at 11pm the night before. Interestingly my TSH was 7.35 but the surgery didn't seem concerned. When I did a Blue Horizon test June 2016 and followed Dr Peatfield's instructions I didn't have any T3 for 24 hours and it was 3.76. To be honest, I'm still confused about the best time to take the last T3 dose before a test for FT3 because there is conflicting advice.

12 hours before the blood test, is the best we can do. 24 hours is too long, and would give a false low.

To be honest that is what I thought. So that would make the second test more accurate which was 4.6. Presumably this result would still suggest an increase in dose would be advisable? I shall ask for another FT3 test tomorrow. Thanks.

Yes, an increase would be advisable! :)



First test:

TSH: 4.52 (0.27 - 4.20)

FT4: 5.7 (12 - 22)

As you are taking T3 only, FT3 should be done every time as this is the only important test. FT4 is always going to be very low or non existent as your not producing nor taking T4.

The TSH shows that you are under medicated. Taking T3 generally lowers or suppresses TSH.

Second test:

TSH: 6.71

FT4: 3.5

Well, this result is even worse considering that you actually took your T3 before the test and proves even more that you are under medicated.

The aim of a treated hypo patient generally is for TSH to be 1 or below if that is where you feel well. And as I said, when taking T3 only the FT3 test is important (no point in testing anything else really) and FT3 should be near the top of it's range.

"What do I say to my GP? "

You tell him what I've said above about FT3 must be tested when taking T3 only. If he doesn't know that then maybe you should be asking to see your endo again, and hopefully your endo does actually know what he is doing when he has a patient on T3 only.

"should I tell my GP about the morning dose for the second test ?"

Does your GP know that your endo's advice originally was to leave off your morning dose? You could explain that to him and you made a mistake and took your T3 before the test so you don't understand why your TSH should be higher. I'm sure your GP won't know either, another reason to go back and see your endo.

"And why did I get a higher rather than lower TSH reading (and lower rather than higher reading for FT4) for the second test? "

No idea why you got a higher TSH the second time.

There will be no reading for FT4 that is applicable. You don't take Levo so not taking synthetic T4 and you are Hypothyroid so producing very little or no T4 yourself. This is why testing FT4 is totally useless and why testing FT3 is so important.

You might want to remind yourself of the replies from Clutter to yourself in this previous post of yours which said more or less the same thing



Two things that comes to mind are

1) You are undermedicated and need more T3 to get your FT3 in the upper part of it's range if that is where you feel well. I imagine that your endo would be the one to authorise this.

2) You may not be absorbing your T3 very well - in which case there are other questions:

a) Are your nutrient levels optimal? Have you had the following t

Vit D




b) Do you take any other medication.

Thank you very much Seaside Sue for your reply. The GP I'm seeing tomorrow is probably the best in the practice and did previously try to get a FT3 test when I saw him with palpitations back in Jan 2016 when my recent problems started. However, the hospital refused to do it and so eventually I did it with Blue Horizon. Then out of the blue the hospital did do a FT3 test (see results above in answer to Grey Goose) with a routine TSH test. However, the critical factor is when one takes the last dose of T3 before the test...

Your other points are all very valid. I have been gluten free for 18 months but I know there have been slip ups which are impossible to avoid unless you never go out and everyone in the family is gf. I am certainly not obviously sensitive to gluten. The nutrient levels are OK apart from folate but I have been taking a supplement recently and need to get it tested. I don't take any other medication. I've been prescribed beta blockers because the palpitations turned out to be supraventricular tachychardia. However, I didn't get on with them and as I have low BP am wary of them. The palpitations then faded away but are back again now. Ho hum.


Previous posts say you have Hashimoto's so are your vitamins at good levels. Are you still gluten free, have you inadvertently been glutened or other food intolerances to consider. Hashimoto's can reduce absorption of the T3 as well as low vitamins

Just to update this, at my appointment yesterday my GP suggested I increase my dose of T3! So I am now on 25mg daily and will have another TSH test in two months. He said to request a FT3 test at that time and hope the hospital do it. I'm amazed it was so easy but the irony is that the higher TSH reading I got (I did not say I had taken a dose that morning) swung it. I just hope that there is a noticeable improvement in my lethargy over the next couple of weeks. Fingers crossed! Thanks again everyone.

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