Thyroid UK
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T3-gap-blood take

What's the best gap to leave after taking T3 before pricking finger? I have twice previously left 12 hours after T3 and 24 hrs after T4 by delaying my morning meds until after pricking and T3 levels have been 5ish mcg. This time, because I have altered my times of medication, I took my T4 and T3 at 4am, then T3 at 10am then a gap of 12 hrs and did finger prick at 10pm. This has shown my T3 to be just over range and T4 higher in range than before. For T4 this is probably because it was only 18hrs after medicating. I was only looking at my T3 level so I'm not bothered with the T4 result.

About 6 weeks ago I managed to obtain my T3 from the GP but I had a third of a foil left of my Turkish T3 left which I decided to use first. I was then taking a total of 18.75mcg T3 with 75mcg T4. (I still had a few aches and pains, but nothing to write home about). Because the mp T3 is such a small tablet to cut up I decided to raise my Turkish T3 to 25mcg then swap tablet for tablet. Some people have felt that Turkish T3 is weaker so this fits in with that thought. When I used up the foil I switched to mp T3. This is when I finger pricked.

FT4 16.83 (12-22)

FT3 7.23 (3.1-6.8)

TSH 0.005 (.27-4.2)

FT3 will now fall because I will only be medicating 20mcg so I don't think there's anything to worry about but next time in a month when shall I do the finger prick? I take my meds at 4am (10mcg), 10am (5mcg) and 4pm (5mcg) with T4 at 4am. When I saw the T3 result I thought it was high having raised from 5.6 to 7.23 for a raise in med from 18.75 to 25mcg. (Still got aches but in my back now not thighs)

Best wishes everyone

4 Replies


TSH and FT3 are approaching their highest levels at 10pm. That, and increasing to 25mcg T3 from 18.75mcg is undoubtedly why FT3 is over range. Most people test early in the morning when TSH is highest. If you leave 12 hours after last T4 and T3 dose your result will reflect normal circulating levels.


I take T4+T3 at 4am, leaving 12 hours would put finger prick at 4pm. Otherwise I could forget 4am dose and finger prick at 8am. This would mean 28hrs after last T4 and 16 hrs after last T3. Would this be ok? A finger prick test at 4am before I take both tablets would be 24hrs after T4 and 12hrs after T3 but what is T3 doing at this time and do I really want to be taking blood in the middle of the night? Next time I'll probably go for missing tablets at 4am and taking blood at 8. Any comments? Thanks Clutter.



I would skip 4am dose and test 8am. If you add +10% to the FT3 result after leaving 12 hours between last dose and blood test you'll get a reasonable estimate of normal circulating FT3.


Great! That's what I'll do when I test in a month. Thanks as ever.


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