Low FT4 High FT3

Hi there, has anyone else experienced labs results similar to this? And if so what do they mean? Was stable on 3 grains thiroyd (for 8 weeks) prior to testing - did not take meds on day of test.

TSH 0.02 mIU/L 0.27 - 4.2 ( 0.051) normal

FT4 * 10.8 pmol/l 12.0 - 22.0 (10.87) low

FT3 6.2 pmol/L 3.1 - 6.8 ( 5.47) high

Any input gratefully received - I am more worried about the low FT4.

19 Replies

  • The just mean you're taking T3. When taking any form of T3 - NDT or liothyronine - you can expect your FT4 to be low. It doesn't matter. :)

  • So not to worry about high T3? Not pooling? Thanks

  • Ah, I didn't say that. Blood tests only test what's in your blood, they don't tell you if it's getting into the cells. The only thing that can tell you that, is how you feel. Do you still feel hypo? Maybe, you might even need a reduction in dose, but only you can say.

    I'm not at all sure about this business of 'pooling'. It's another of these words that people bandy about on thyroid forums, without really knowing the implications. So, it's not something I would really pay much attention to, myself.

    However, you are on a decent dose of NDT, so it doesn't surprise me that your FT3 is up near the top, and the FT4 is low. The body only keeps what it needs, and when you're taking T3, it doesn't need so much. That's all.

  • Thanks, I am not sure about the whole pooling thing either. Still have brain fog (main symptom) - I don't feel overmedicated, but not sure I want to raise any further either. Will hold for a while I guess and see.

  • brain fog can be caused by all kinds of things including low b12.....so don't assume it is from being hypothyroid. I wouldn't take any more ndt and if you start having heart paps or anxiety or feeling a little hyper or anxious, then go down a little.....

  • Thanks, my B 12 is in good shape at the moment. Not anxious and no palps, like I said I do not feel overmedicated, neither do I feel the need to raise. Might try T3 only.

  • Why would you switch to a synthetic? It gives a bumpy ride compared with ndt. Its not the same. Have a read of this.... Then decide.



  • Too much T3 causes brain fog too. Ask any Graves' patient.

  • If you think you're pooling, you should read this: tiredthyroid.com/blog/2015/...

    Your labs are common in someone who is taking too much T3 and not enough T4. NDT has a higher ratio of T3 to T4 than what a human produces, so your high FT3 and low FT4 simply reflect your medication's contents. T4 is essential to normal brain function, and your low FT4 may explain your brain fog.

  • As reliablerebel is taking natural dessicated thyroid hormones, her results cannot possibly be the same as someone taking levothyroxine alone. Levothyroxine was introduced along with blood tests. Levo is T4 only. NDT has been in use since 1892 and no blood tests were invovled, only clinical symptoms. With NDT having T4, T3, T2, T1 and calcitonin, using blood tests which are for the use of levothyroxine cannot correlate.

  • That was my point, a patient's lab results reflect the medication they're on. If on T4-only, T4 will be high, and T3 will be low. If on NDT, then T3 will be high and T4 will be low. Neither reflects a HEALTHY person's results, which would be somewhere in the middle or higher for BOTH hormones. There are some excellent charts on this page which illustrate this: tiredthyroid.com/rt3-3.html

    You and I disagree on many points, and that's okay. Everyone's viewpoint is created from their own experience. You feel well on T3-only, so your advice reflects that. I did not feel well on high levels of T3, so my advice reflects that. I want patients coming here to have access to both points of view, because getting well is the goal, it doesn't matter which route they take. Patients should know that there is more than one type of medication available, and that they can be taken alone or in any combination.

    While some things are opinions, like which protocol is best, there are some facts that I feel are misrepresented. T4 is not just a prohormone, it is not inactive, and there are T4 receptors. There are medical studies that support this. Just because someone like Dr. Lowe said it doesn't make it true. I could probably quote a lot of other doctors who believe a normal TSH means any remaining symptoms you have aren't thyroid related. We all know that's not true.

    You help patients who come here by educating them about the T3-only protocol. If they have already tried T4 and NDT, it is helpful for them to know that there are people like you who do well on T3-only. They may not have even considered that option. I, on the other hand, will speak up when I see someone floundering and it appears to me that they're taking too much T3. They may never have thought of combining NDT with T4. We both have the same goals, patient wellness, but we have different experiences we're drawing from. Peace.

  • Your results look exactly as one would expect from someone taking a medication containing T3. Low FT4 is nothing to worry about if you are on T3 or NDT. The main function of T4 is to be convertd into T3. If you are taking enough T3, your body doesn't need to make any/as much T4. Your FT3 is high in range but not over range. If you feel good, I wouldn't change anything. The ranges were introduced for people taking levo only.

  • Thankyou, I suppose that is what I was thinking also, but needed confirmation x

  • I recently had some bloods back and my FT3 was higher than I've known it to be, I'm on NDT But I had aching muscles which I'd put down to having to take Letrozole and knowing that is a side effect so I dropped down very very slightly, one quarter every third day and muscle pain disappeared! So it can be a very fine line and not easy to work out always whatcis doing what but my endo says not to worry about FT4 or TSH and that mirrors my logic.

  • Thanks for that. Lucky you have found a good endo they are hard to find. I have no other symptoms of being over medicated, but dropped right down to one tablet for 10 days to try to clear the FT3 a bit. Now going to go back up to two and maybe hold there. My labs were pretty much the same on 2.5 grains, FT3 high and FT4 low. But even more of a gap on 3 grains. So might see how I get on with 2 for now.

  • Was your FT4 below the reference ranges?

  • I haven't gotvthem to hand at the moment but don't think so. Probably about the middle of the range or I would have remembered. I seem now to have been passedto one of the consultants team as he knows I can work out or at least ask if I'm concerned! However the new chap tried to tell me my TSH was too low and we had a bit of banter over that until I asked how did he know my pituitary is working properly? ! Still I had to listen to the risks to my heart, bones etc!! I did tell the endo what he had said so I hope he's sorted him out before my next visit!

  • I don't understand the above. I read that your FT3 is 6.2, and the normal range is 3.1-6.8. So why were you told that you are "high"? What does the trailing "(5.47)" mean?

    Thiroyd is NDT, which contains T3:T4 in the 1:4 ratio. In the human body, the "natural" ratio is higher, up to 1:20. So you are getting "too much" T3, and "too little" T4. But if you feel well, it doesn't matter, since T3 is what makes you feel well. If you think you could feel better, and suspect your body is capable of converting T4->T3 (some people cannot do this), then it is possible that reducing your Thiroyd dose, and adding in some T4, could be a positive change. Just remember that medicine is an experimental science; the only way to find out if this might benefit you, is to try it. If you are able to convert, then having more T4 would reduce the peaks and valleys of the (varying) T3 level in your bloodstream.

  • I'm very confused by this thread.

    Your FT3 result is not high. It is within range?

    My endocrinologist would not call it high. He would call it within range.

    Why are you concerned?

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