Does anyone know the best time to get T3 checked please ?

I know TSH is better done as early as possible in the morning .Having TSH and T4 done on the NHS but can only get T3 done at the private hospital . In 10 years I have never had T3 checked so because I never feel well thought I should get it done . Over the past few weeks I have been experiencing anxiety on waking ,and sweats and flushes during the day . My last TSH was done a couple of months ago and it was 0.39 ( 0.37-4.5) been on 125/100 alternate for a few years now . Should add it's 10 years since I had a period so don't think it's the menopause .

6 Replies

  • My GP just ordered the FT3 test and I was thinking of posting the same question. It took me few times of asking different GPs though to get them to agree to it. I googled it quickly and didn't find a lot if info but apparently it fluctuates a little bit, but nothing like TSH. So probably morning is best, but it will not make a huge difference if you do it later. I hope I'm right...

  • Thank you Piret ,it's not my Dr it's the labs that refuse ,he is bemused by it as much as us .

  • actually my GP said as well the lab might refuse.... but he said hopefully not - we'll see. It's baffling how labs can just do that?!

  • I've never seen anything to suggest that timing of blood draw affects FT3 results. FT3 peaks approximately 90 minutes after TSH peaks. The reason for suggesting early morning TSH testing is because TSH is highest early a.m. and this can boost patients into the range which GPs will consider necessary for medication. Conversely, those self medicating and wanting to disguise the fact from their GP would be better having TSH tested at 13.00 when TSH is lowest. :)

    Labs will often decline to test FT3 and sometimes FT4 when TSH is in range. GP can insist by making a note on the bloods form that it is needed for further diagnosis or by picking up the phone and saying the same thing :)

  • both TSH and fT3 are at their highest very early in morning (ie 1-2 am) and both go low in the evening.

  • I'm wondering if there's a conundrum here - if those of us whose TSH is always in range but suspect problems with T4 to T3 conversion have the TSH done at the optimal time and the values rise to just above the range, that would spur the labs to test FT3. However this would be at the highest value too, which then contradicts the low FT3 argument.

    I recently tried to get a phlebotomist to draw bloods as near to midnight as poss but when she checked with the labs they said that timings for TSH are irrelevant so she ended up taking the bloods at 7.30am. Needless to say the results were (yet again) in the middle of the range.

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