Thyroid UK
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Optimal FT3 after 12-hr fasting?

Hi everyone,

I had a call with my endo the other day and he says that with TSH = 0.006, FT3 = 4.48 (2.63-5.7), FT4 = 11.5 (9-19), TT3 = 1.54 (0.89-2.44) I could be a tiny bit overactive (he wants me to hold the dosage, but might ask me to decrease by 1/4 grain in a couple of months...). He also says that FT4 would be low when taking NDT, but in many years that never happened to me...

What is your FT3 after 12 hour fasting? Is mine typically low? I am still tired, wake up in the middle of the night most nights, hardly digest anything, skin is dry. I take 2.5 grains of Nature Throid.

Thank you! :)

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Fasting overnight before blood test is to do with TSH. When someone is looking for a diagnosis, an increase in Levo or to avoid a reduction, TSH is needed to be high. As eating lowers TSH then it's recommended to fast overnight to try and get TSH as high as possible. It won't be anything to do with FT3. The time you take your dose of T3 containing thyroid meds determines your FT3 result mainly.

NDT does tend to lower FT4 and yours is low in range, where it's expected to be.

As Clutter mentioned in your last thread, if you don't feel well there is room to increase your dose of NDT. With those results, I wouldn't be reducing dose.

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Thank you :) I was on 2.75 and 3 grains and felt awful, reduced to 2.5 by endo's advice (slightly over range ft3 at the time), but now it seems that my ft3 and ft4 are lower than 2 months ago even though I am at the same dosage - would this be a sign to increase? I wish I had an endo that doesn't look at lowering tsh from 0.006...my pulse is 55-64.

My feeling was also that I shouldn't reduce to be honest...

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I didn't do well on NDT so I can't advise on dosing from experience. I thought dosing with NDT was more about how you feel. However, if your endo is NHS then does he really know enough about it or is he just going by TSH like most of them do? They don't seem to understand results when using T3 so I doubt they know much about NDT.

Also, the fact that you have Hashi's complicates things because the antibody activity is going to make your results fluctuate.

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You're right, my previous GP, who had me a 4 grains (I think he might have overdosed me though), told me it's about how you feel, pulse, temperature, mood etc, but he passed away and now I go to an endo who looks at tsh, but also ft4 ft3. I think I will just treat myself. My Hashi's is quite bad, over 800 where the range is 0-5...thank you again, just confirm I need to change certain things. I live in Ireland and he is a private endo.

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He also says that FT4 would be low when taking NDT, but in many years that never happened to me...

But, your FT4 is low. It's not even mid-range.

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that's right, I am questioning his beliefs :) going back, I never had ft4 so low on NDT, my symptoms start pointing to hypo. According to what everyone says and research, ft4 should be mid-range minimum...

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I don't think anyone says that when you're on NDT. FT4 will be low when you're taking any form of T3 because the body only hangs on to what it needs, and it doesn't need as much. Your endo is right about that. It's when you're on T4 only that FT4 should be mid-range minimum.

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oh okay...it was never the case before so I questioned him. thanks for clarifying it for me. would it be correct that I take a bit too much according to him if body only hangs onto what it needs (so my tsh is low while my ft4 and ft3 drop)? sorry if this sounds silly...

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It doesn't sound silly, but I'm not sure I understand it. If your body doesn't hang on to it, it won't have any effect on your TSH, it's the T3 in NDT that causes the TSH to go low.

It doesn't matter about the level of your FT4, it's the FT3 that is important. And that is saying that you need an increase in dose. Or, if you don't want your FT4 any higher, the addition of a little T3.

Your endo is only looking at your TSH, which is totally irrelevant, but he doesn't know it. It's a sad fact that endos, for the most part, know nothing about thyroid. So, you are not over-medicated in any way (you can't be hyper, because you're hypo, it can't go backwards!), but you could be a little under-medicated if you still don't feel well.

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Thank you Grey, this is very helpful! I will increase by a quarter and hold for a while to see what happens. It also seems completely logical that maybe after a while of taking same dosage, one needs an increase if ft3 drops :)

One more question - I used to split dosage, but I don't absorb stuff well due to indigestion etc which is getting worse and worse. I took the whole dosage of 2.5 grains on empty stomach today and I felt adrenaline was rushing through my veins, then it settled a bit, definitely more energy, would it work that quick that active t3??

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I find it difficult to believe it would work that quickly - certainly it never has for me - but some people insist it does. So, who am I to argue! :) If it works for you, then great! Go for it!

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this could be my head, it did that before :P I will give it a few days, hopefully it settles and then raise the dosage :) thank you so much!

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I have absolutely nothing again the placebo effect! If it works, it works, never mind how. lol :D

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:D :D :D

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Hey Grey! Hope you're well :) It's been 2 weeks since I have increased by 1/4 grain. I wonder if I can go higher by 1/4 again or need to wait 4-6 weeks? It feels a tiny bit better. I remember my old doc said that he seen people doing well having an over-range ft3 (if range is up to 6, he said 8 or 9). Also, would I be correct in saying that if you take a lot of NDT at once for a long period of time your body can't cope, because of such a dramatic increase, but if you increase slowly you might get to that dosage and more as your thyroid is adjusting, if it makes sense? Thanks as always, very grateful :)

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I think you need to wait and get retested. Your FT3 was quite near the top of the range, and you don't want to push it too far over. I'm not sure of the wisdom of your old doc's advice. An FT3 of 9 when the top of the range is 6, seems much too high to me.

It would be correct to say that you need to increase slowly, so that your body can adjust, yes. That's true of all hormones. Start low and increase slowly. But, it has nothing to do with your thyroid adjusting. Once you are on thyroid hormone replacement at that level, your thyroid is completely out of the loop. NDT doesn't do anything to the thyroid itself, it's the rest of the body it affects.

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Thank you :) I will wait then another 4 weeks and re-test. that's true, it seems my FT3 is dropping over the last few months from where it was, this is why I was wondering if my body (not the thyroid ;) ) adjusted and had to go up a dose. Previously I was put on 3 grains straightaway after a month break (!). Also, a month break affected me very badly few months down the line...

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We're not really supposed take breaks!

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