T4 or FT4 ?

What is the difference ?

My GP here has always measured FT4 and FT3 for me ? However, I was in India for a few months and got one blood test done there.

They measured T4 and T3 and TSH levels and not FT4 and FT3 ?

Also, I was reading a WIKI article on Levothyroxine and it says something to the effect of Levo(Supplemen) being a Hormone suppressant ? This, I am unable to comprehend. What exactly is the function of Levothyroxine ? Also, how could it be related to increased risk of Osteoporosis.

19 Replies

  • Sat77, T4 and T3 can be measured as total T4 and T3, and free T4 and T3. Total is the T4 and T3 bound to proteins. Free is unbound T4 and T3 available for cellular use. Total is rarely used by the NHS now, with Free T4 and T3 being favoured although private labs offer both.

    Some labs abbreviate the FT4/FT3 to T4/T3 but the ranges will make it easy to distinguish. Total T4 would look something like (59-165) whereas Free T4 will be something like (12-22) and similar differences for Total T3 and Free T3.

    Levothyroxine is hormone replacement it's not a suppressant. It's function is to raise T4 and T3 and lower TSH in hypothyroid patients. Long term overmedication with FT4 and FT3 over range increases the risks of osteoporosis and atrial fibrillation.

    Carbimazole and PTU are anti-thyroid drugs which are T4 and T3 suppressants for hyperthyroid patients.

  • Most of the T4 and T3 in your blood is attached to various proteins. That is called "bound" T4 or T3 and is measured in a Total T4 or Total T3 test . A tiny amount is not bound and that is called "Free" - that is what is measured in a Free T4 or Free T3 test.

    In many ways, you can think of Total T4 and Total T3 tests as being related to how much of the binding protein you have rather than a useful thyroid hormone measurement.

    However, when you see reference to a T4 or a T3 test, you simply do not know which test it is - Total or Free. You have to look further - check the reference ranges, the results, the units.

    The intention of taking levothyroxine is to restore your thyroid hormone levels. Unfortunately, if you take a small dose of levothyroxine, it can reduce the amount your own thyroid makes but not provide enough to make up for that reduction. We see a lot of people who don't do at all well on 25 micrograms, or even 50 micrograms. Some do much better when they take more - maybe 100 micrograms.

    Osteoporosis has been seen in people with very high T3 levels - such as occur in Graves disease. There is no evidence that ordinary, sensible amounts of levothyroxine will cause osteoporosis. There is evidence that sensible levels of thyroid hormones improve bone health.

  • This has interested me , I've been taking 25 mcg for over 2 months now and feel worse than before they have it to me, I'll be bringing this up with my doctor tomor

    I don't think he will raise it mind so in wondering whether to stop taking it altogether!!

  • You mention tests but do not appear to have posted any of the results. Do you have them? Would you post them?

  • I've posted them previously, before I started medicating my tsh was 2.24 can't remember range sorry, and my ft4 was 10.5 range was from 11-22

    They werent going to treat me but I was severely symptomatic, hence the 25 mcg levo

    After 4/5 weeks I felt no different so started self medicating with t3, that was 4/5 weeks ago, I was taking 25 mcg and had an ft3 test, my level was 5 and the range was 3.9-6.8 (I think) I've got them written down somewhere but I'm in bed now!!!

    But my gp tested my tsh and it was 0.14!!! So I'm to carry on with the minute dose of levo!!

  • You have hit one of the problems with self-medicating, I'm afraid. Could you come clean to your GP?

  • Yes I have an appointment tomorrow, I just haven't been able to get to see him to tell him until now!

    Although I'm not sure it will make any difference to my medication! X

  • He may not increase the Levo, but it doesn't matter, because you can keep increasing the T3. That's the important one.

  • Grey goose I could cry, I thought this doctor was fantastic but I was a few minutes late (but he did have a patient with him anyway?

    I explained that I'm still dead on my feet, my hands swell s d I feel like I have flu constantly aching, he said X Ray and bloods, and then 'sorry to rush you cut you were a bit late' I didn't even get the chance to tell him about the t3!!!

    I have no idea where to go from here now x

  • Carry on as you are, do the xrays and bloods and let us know the results. Did he say what he was testing for?

    That was a bit off of him behaving like that. You may have been a bit late - can happen to anyone - but he did take another patient in, so there was no reason to cut your rdv short. :(

  • He usually goes over on his time, he usually gives patients more time than you should, but I think he was trying to play catch up with me, my appointment was 9:20 and his 9:30 was there, I didn't go in til 9:30 so he had run over on previous patients!!! I'm not happy at all,

    He said 'chronic fatigue' I didn't even have chance to ask him to test my vitamins!!

  • Natj, it looks to me like you are on the right track by sourcing your own T3 and self-medicating! You've been very brave so far! Especially if I'm reading you right and you're in bed and struggling to researhch and read. The ppl on here can give you good advice about how to adjust your dose.

  • Thank you silver avocado!

    I have to get out of bed as I've got a 5 year old and 1year old !

    But I basically lay on sofa all day!

    I'm in tears by the time I get my daughter to school and I'm lucky enough to drive!

    The school ate good with me mind , I burst out crying to teacher and I explained my struggle and they are lenient with my time keeping because basically I have no one else to take them!

    And by the looks of things they don't take me very seriously in the surgery, I feel like I'm wasting their time, I've struggled the past 7 years and been back and forth and I actually refuse to see one gp because he said to me 'so what are you complaining about now'

    My husband was furious

    I would change surgery but they are really rubbish the other ones!! I feel like this group is the only help and support I have now!!!

  • Well, we're here for you, Nat. Take no notice of their attitude. You are the intelligent one! And refuse to accept a 'diagnosis' of Chronic Fatigue, it's meaningless!

  • It's like the 'ibs' diagnosis isn't it??

    I came out close to tears!!

    I just can't believe it!!

    Thank you grey goose 🙋🏾 x

  • You're welcome. :) x

  • In my prayers, I will ask the lord almighty to give you strength enough to take care of the family during these tough times, and have faith, there is light at the end of it.

  • Oh thank you sat 77 I really appreciate that , it's meant a lot to me!!!

    To be honest if it wasn't for my kids I probably would've given up but I actually can't, they need me, admittedly in not the best mother but I'm doing my best :-) many thanks xx

  • Long term replacement of thyroid hormone has not been shown to cause osteoporosis, but people who make too much hormone, as in people who are hyperthyroid, do run the risk of osteoporosis. Here is a paper about this.... ncbi.nlm.nih.gov/pubmed/825...

    Levothyroxine and liothyronine are replacement hormones. If you take sufficient amounts then there is no need for your thyroid to produce hormones and the tsh drops so the thyroid stops making them. The worst case scenario is whn people are given enough meds to stop their thyroid, but not enough to make them well.

    The function of levothyroxine is that it is an inert storage hormone containing 4 iodine atoms. when we need more energy the thyroxine has an iodine atom removed and it then becomes the active hormone t3. (Triodothyronine).

    X. g

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