Thyroid UK
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Going to sound really thick here, but why do some folk have 'block and replace'?

Sorry for being thick, but a I've a few related questions due to my lack of understanding of (my) Graves Disease:

What is 'block and replace' and why do it? Why not just block using different doses of Carbi?

How are 'desired' levels for people reached?

How do you know when your levels are right?

I can't really get my head around the whole T3, T4, TSH thing. The only thing I understand is that TSH level being too low to measure is 'bad' and that very high levels of (erm - trying to remember here) T4 are 'bad'?

I just know that I don't want to have either the RAI or surgery that my Endo is pushing for (or to be gaining so much weight)!!

Is there an 'Graves Disease for Dummies' guide? I'd like to think that I'm a fairly intelligent woman, but my mind fogs over when reading up about this...

Sorry for long post.

10 Replies

Typical signs of Graves in blood work are low or even no TSH, High levels of T3 and T 4. The treatment with carb is to try ans slow down thyroid production so T3 and T4 levels come down.There are ranges( between higjest and lowest) where they like them to be, Therefore the aim of carb is to get them back down into range.

Some Endos prefer carb on its own others prefer block and replace , this is blocking all production of thyroid hormone by larger amounts of carb then giving back thyroxine with the idea of keeping you steady, No particular way had been shown to be best.The endo will say your levels are right when they come in range ad explained above, You will also most likely feel better then too.When you are in range people then usualky after some months stop taking the meds to see if theh can feel well and stay in range without treatment,

Unless you have regular tests you will not know if you are in range or not but usualky peopke knowcwith how theh feel, Hope that helps a bit x


Thanks so much. The reason I was wondering about the 'desired' levels as my endo keeps on about TSH being unmeasureable. When I saw her on Thursday, she told me to up my carbi dose again (I had commented on another thread about this). She wants me to put it back up to 25mg. I'll try and find the link and post.



I commented on this post -



Thyroid Stimulating Hormone (TSH) is produced by the pituitary gland to stimulate the thyroid gland to produce thyroxine (T4) which is an inactive pre-hormone which converts in the thyroid gland, liver and kidneys to the active hormone triiodothyronine (T3). T3 is needed in every cell of the body.

In hyperthyroidism excess T4 and T3 are produced and the pituitary gland suppresses the TSH in an attempt to shut down the thyroid gland's production of T4 and conversion to T3.

Blocking with Carbimazole starts with a high dose which is titrated until thyroid blood results are within normal range (euthyroid).

Block and replace involves a high enough dose of Carbimazole to block production of T4 and T3 ie rendering the patient hypothyroid and a compensatory dose of Levothyroxine to treat the hypothyroidism.

'Desired' levels are when thyroid bloods are within the lab ref range (euthyroid). Monthly monitoring on Carb avoids the patient becoming overmedicated and hypothyroid. You'll 'feel' right when you're euthyroid ie hyperthyroid symptoms are controlled and cease.

A member posted this week that he had been on Carb and successfully avoided thyroidectomy and RAI for 10 years so don't allow your endo to push you into surgery/RAI unless Carb or B&R aren't working for you.


Clutter can they do block and replace for hashimotos


No, Mauds Carbimazole is to block thyroid over production in hyperthyroid people. You're hypothyroid and therefore not producing enough thyroid hormone.


Thanks clutter


Thanks for this clutter. I found the links you posted really useful too.


because block and replace should mean they can keep your levels stable while completly blocking the overactivity of the thyroid

it will only work if your able to tolerate thyroxine abd such a high dose of carbimazole but personally i think its a chemical cosh


Im on B&R for about 1 and 1/2 months now and recently I feel as low/depressed/hopeless/lost as I did before I was diagnosed. I wish they would just take the stupid thing out!


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