When replacing with T3 will T3 blood test results be higher than 'normal' range?

Hello lovely people,

I'm wondering if when you are taking T3 could this lead to higher results for T3 blood tests than those of people who don't have thyroid issues, or who are taking T4 only?

I understand that the more thyroid hormone you take the higher the results will be, so taking more T3 and less T4 will lead to an increase in T3 levels and a decrease in T4 levels. But what I mean is, do the ranges still apply the same way depending on what you are replacing with?

Some more information for those who want it:

I am taking both T3 and T4 and am slowly increasing the T3 while decreasing the T4, with the possible aim of being on T3 only if that's what makes me feel better.

So, I was on 125mcg T4 and 20mcg T3 and my blood test results were:

TSH 0.01 (Range 0.3-5)

FT4 14.3 (Range 9-21)

TT3 2.7 (Range 0.9-2.5)

My endocrinologist was not happy with the 'raised' T3 result and said I was over replacing. I don't have any hyper symptoms and each increase of T3 has made me feel so much better, and I'm personally not particularly concerned at being 0.2 over range, but for now I shall play ball with the Dr's and do what they say as long as I continue to feel better.

Anyway, he reluctantly agreed to let me increase my T3 to 25mcg if I dropped my T4 to 75mcg, which I'm happy to do and feel fine on so far.

Thanks to everyone for reading :)

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11 Replies

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  • Kittenmittens,

    Total T3 (TT3) isn't commonly used in the UK, most labs use Free T3 (FT3). Certainly T3 levels should remain within FT3 range.

    The more T3 you take the higher your FT3 level will go. If you take T3 only FT4 will drop below range.

    5mcg T3 is equivalent to 15mcg Levothyroxine so you've actually had rather a large decrease in dose and are unlikely to feel any benefit from increasing T3 from 20mcg to 25mcg.

  • Hi Clutter, thanks for the reply. The labs my GP's use and the hospitals use won't do a FT3 test, I have asked. I'm lucky if I get any T3 results at all, the computer system for blood tests doesn't even have a tick box for it so the Dr's have to write it in as a request and half the time it doesn't get tested regardless.

    The Endo wants me to increase the T3 in 5mcg increments and I had to drop my T4 to go up by the latest 5mcg as my T3 bloods were over range. I'm fine with that as the Levo hasn't worked for me anyway and dropping it doesn't seem to have much of an effect. Whereas the T3 increases overall are really making a difference.

    But what I really meant by my question was do the ranges still apply in the same way if replacing with T3 and T4, as T4 levels will drop and T3 levels will increase?

    For example,

    a) a person not taking thyroid hormones, or someone just taking T4, had a result of 50% T4 and 50% T3. The 50% of T4 would convert to T3 leading to 100% T3.

    b) a person taking less T4 and more T3 might have a percentage of 25% T4 and 75% T3. Again the T4 would convert to T3, leading to 100% T3.

    But in example b) there would be a higher % of T3 currently in the blood, meaning the ranges might not apply in the same way.

    I know this is not the science of it AT ALL! Haha, but just trying to use this example to try and explain what I mean. no idea of I've made myself an clearer or just made it more confusing!

  • Kittenmitten,

    T4 converts to T3 and rT3 so T4 doesn't convert to 100% T3. There will be a higher percentage of T3 in the blood if you take more T3 than T4 or all T3.

  • Thanks Clutter.

    Yeah, I knew the actual science bears no relation to the example! it was more an illustration to try and explain what I was getting at :)

    And, that's what I mean, there will be more T3 in the blood when replacing with T3, so do the blood test ranges still apply the same way? As they are more designed as the ranges for those with a functioning thyroid who will be producing the expected amounts of T4 and T3.

    I just wondered if the method of replacement would mean the ranges don't apply the same way?

  • Kittenmittens,

    The ranges still apply ie if you only take T3 your T3 level should remain within the FT3 range your lab uses. I don't know whether the same applies to TT3 range as I'm not familiar with TT3.

  • Thanks Clutter :)

  • How long a gap did you leave between your previous doses of T4 and T3 before getting the blood sample taken?

  • hi Humanbean, thanks for the reply. I think when the bloods were taken was problematic this time. Normally I book my blood tests at 9.00 in the morning, meaning I haven't taken any T4 for 24 hours and haven't taken any T3 for 16 hours, and I fast too. But this time the Endo took my bloods at the hospital in the early afternoon and I not long taken my T3. In future I'll be prepared for this eventuality and try to make sure I have left as big a gap as possible between meds and blood tests.

  • Remember you are testing the hormones in your blood, not how they got there and you must kern the FT3 in the range but it may be you didn't stop the T3 12 hours before the test so that's an important point that's been raised. I once went over with T3 and didnt feel good but I had passed my 'sweet' spot and was then feeling the effects of being over medicated. Dropping it down a little may well prove that to you. Endo's though try to drop you a little further and then let you raise somewhere in between if deemed necessary. I'm taking NDT but have worked out that every third day I take a little more but the fine tuning is the difficult bit I do find.

  • Hi Silverfox, thanks for the reply. Yeah, I had taken my T3 too close too when I got my bloods done, so I'll try and prepare for that in future. I felt fine on the T4 at 125mcg and the T3 at 20 mcg, even though my bloods showed I was over range. So it could be that I am okay with my T3 levels slightly out of range or it could be just that the blood results weren't that accurate due to having recently taken my T3 tablet.

  • Mistakes aren't a problem as long as we learn from them! But T3 should never be above the range though as you say taking your last dose too close to testing is more likely the problem. Just remember that though if your next test is over range then drop it by a quarter.

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