Just need a sanity check.

[NotAllWhoWonder]

I feel like I've learnt a LOT from everyone here, as well as the resources they've recommended. A huge thank you to all of you! Oddly, I'm still coming to grips with some of the basic concepts, though, so just thought I'd check to see whether or not I'm understanding the whole physiological process behind everything properly.

So, basically, the pituitary gland produces TSH, which tells your thyroid gland to produce T3 and T4 (approximate ratios are 10-20% and 80-90% respectively). T3 is the active form, which is used by multiple functions in the body. T4 can also be converted into more T3 by the liver. This all runs on a negative feedback loop, so if T3 and T4 are low, the pituitary gland produces more TSH, which makes the thyroid work harder. TSH then drops according to what the levels of T3 and T4 in the blood are, and the thyroid produces less.

With hypothyroidism, the thyroid does not produce sufficient T3/T4, regardless of how much TSH the pituitary gland pumps out, so treatment with levothyroxine is needed, which is pure T4. So the assumption is that the entire load will fall on the liver to convert it to T3? I read somewhere that something is required to complete the conversion, so if I'm deficient in that or have some sort of liver problem, the levo isn't going to make a difference?

[tattybogle]

conversion is 'mainly' in the liver , not 'just' the liver.

The first 2 replies to this post are quite informative : healthunlocked.com/thyroidu...

Jim's reply leads to this paper , which gives more details on where in the body T4 is converted to T3 : onlinelibrary.wiley.com/doi...

[greygoose]

T4 mono-therapy makes a lot of assumptions! Firstly that everyone has a perfectly functioning pituitary. Secondly that everyone absorbs through the gut perfectly - so many reasons why they might not. Thirdly that everyone converts perfectly - so many factors that can affect conversion so that's not true, either. I'm sure there are many other assumptions but I can't think of them for the moment.

[SlowDragon Administrator]

Also important to maintain GOOD vitamin D, folate, B12 and ferritin for good conversion

Many patients find it important to always get same brand levothyroxine at each prescription

If thyroid issues are autoimmune, gluten free diet and/or dairy free diet often beneficial or essential

[NotAllWhoWonder in reply to SlowDragon]

I’ve been tested for the antibody and it came back negative, so hashi is unlikely, right?

[SlowDragon Administrator in reply to NotAllWhoWonder]

Not necessarily

Have you had BOTH TPO and TG antibodies tested?

Any autoimmune diseases in your family

About 90% of primary hypothyroidism is autoimmune thyroid disease, usually diagnosed by high TPO and/or high TG thyroid antibodies

Autoimmune thyroid disease with goitre is Hashimoto’s

Autoimmune thyroid disease without goitre is Ord’s thyroiditis.

Both are autoimmune and generally called Hashimoto’s.

Significant minority of Hashimoto’s patients only have high TG antibodies (thyroglobulin)

NHS only tests TG antibodies if TPO are high

20% of autoimmune thyroid patients never have high thyroid antibodies and ultrasound scan of thyroid can get diagnosis

In U.K. medics hardly ever refer to autoimmune thyroid disease as Hashimoto’s (or Ord’s thyroiditis)

[Tina_Maria]

Thyroid treatment is based on the assumption that when you give levothyroxine, all your needs are met and that you will get back to normal. It also assumes, that the pituitary feedback hormone TSH is working in a hypothyroid patient just like it does in a person without thyroid disease. Sadly, this is not the case and this is where the problems start.

There are 2 papers that describe that the TSH-T4 axis in hypothyroidism is not responding as it does in a person without the disease. Therefore, the TSH should have a supporting role and certainly not a prominent role in treatment decisions for patients.

pmc.ncbi.nlm.nih.gov/articl...

frontiersin.org/journals/en...

In conclusion, pituitary TSH cannot be readily interpreted as a sensitive mirror image of thyroid function because the negative TSH–FT4 correlation is frequently broken, even inverted, by common conditions. The interrelationships between TSH and thyroid hormones and the interlocking elements of the control system are individual, dynamic, and adaptive. This demands a paradigm shift of its diagnostic use.

[NotAllWhoWonder]

Thanks for all the replies! Feel like I'm learning a lot more here than anywhere else.

I know that TSH isn't the best measure for what's happening with my thyroid, which is why I'll order some private tests when I get back from Australia mid January so I can see the numbers that matter: T3 and T4. Until then, though, I'm still reliant on my GP making dosage adjustments based on my TSH reading. Got my latest one in today, and it's 4.56 "Abnormal" (range is 0.27-4.2). I'm currently only taking 25mcg, which apparently is always going to be too low for any significant improvements. Would it be recommended that he increase the dosage based on that TSH reading?

[tattybogle in reply to NotAllWhoWonder]

correct .... over- range TSH is a clear indication for dose increase (to 50mcg) , take that for 6 -8 wks .... retest.

[NotAllWhoWonder in reply to tattybogle]

Thanks!

So, once the dosage is increased does it matter where I end up within the “normal” range? I’ve previously gone all the way down to like 0.19 just on the 25mcg, but I guess the fact that I’m now over range on the same dosage means it’s not working like it should anymore.

[tattybogle in reply to NotAllWhoWonder]

more like 'it's not enough ' rather than 'it's not working'

what happened could be :

when u first added levo ... TSH ( pituitary) 'noticed' the increase in fT4 level and lowered to 0.19 , lower TSH then lowers your own production of T4 from thyroid .

leading to lower overall fT4 level again ... pituitary notices fT4 levels fallen ,, and TSH starts to rise again .

TSh can take a long time to settle down and show the true picture after dose increases....... bit like pendulum singing too far when you push it , then swinging back . kinda thing.

as a general rule , you're looking for a dose that keeps TSH under 2 and staying fairly stable. . some are ok there,, some will need TSH a bit lower.

obviously it's not ideal just having TSH to go by , but at this point it is 'good enough' as an indication of what you need to do next .