Thyroid UK
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Block and replace bloods

Was on 100 mcg Levo and 40 mg Carbimazole block and replace. Reduced to 50 Levo and 40 Carbimazole to see how I coped.

Falling asleep at work, aches and pains in all joints, very weepy and generally not feeling well. Bloods test results:-

Free T3 4.0 pmol (3.5 - 6.5) previously 6.5

Free T4 9.3 pmol (9 - 24) previously 19.3

TSH 1.6 mu/L (0.35 - 5.0) previously 0.03

Annoyingly the GP had market on the blood test request "not on thyroxine"! What is the matter with these folk?

Seeing Endo again 20th August but just wanted to know my next step. I think I am either looking to reduce my Carbimazole to 50% (i.e. 20mg) to level out the reduction on Levo from 100 mcg to 50 mcg or increase my Levo back up to 100mcg.

6 Replies

Pingpong, the 40mcg Carbimazole will make you hypothyroid which is why you were prescribed 100mcg Levothyroxine. Your symptoms are very hypothyroid. Did they happen before or after you reduced your Levothyroxine to 50mcg? I suggest you increase to 100mcg and discuss with your endo whether Carbimazole and Levothyroxine can be reduced.

Were your blood tests done before or after you reduced your Levothyroxine? Your TSH is a little higher than most hypothyroid patients are comfortable with, usually TSH just above or below 1.0 is comfortable and your FT4 and FT3 have dropped considerably. Your previous thyroid blood tests were better in my opinion.

Your GP probably said "not on thyroxine" to persuade the lab to test FT4 and FT3 in addition to TSH.


Hi Clutter,

Symptoms of hypo came on six weeks after the reduction in Levo. I believe his aim will be to reduce my Carbimazole this time. Blood tests this time first after reduced levo, reduced levo from 100 to 50 on 5th June, Blood Tests done 1st August, so eight weeks of reduced levo and six weeks of rotten symptoms.

I was feeling very well and symptom free on my previous regime of 100 Levo and 40 Carbimazole. Endo is guinea pigging me to see whether I can tolerate the reduction first in one and then the other. Just want to go back to feeling good.


Pingpong, Well that experiment was a big fail! I wonder why he didn't reduce both or even just reduce Levothyroxine to 75mcg.


He's the chap that when I was doing well on 40mg Carbimazole suddenly reduced me to 20mg with disasterous results. That's when I ended up on 100mcg of Levo which he said I had to take before I left the hospital:) He does tend to go in big leaps.


Sounds a bit strange to be cutting your levo but leaving you on the same amount of carb, it is quite powerful stuff and like clutter says you could end up hypo.

I was on block and replace and stayed on 40mcg Carbimazole all the time, I started on 50 mcg thyroxine and had it gradually increased until I was taking 75/100 mcg on alternate days. I found I felt bad every time I needed an increase in my levo. When it came time to stop the B&R I stopped both Carbimazole and thyroxine right away - both at the same time.

Why don't you go back to your GP and say that you are feeling REALLY ill, you can't go on any longer, you know that you were feeling very good before the endo started messing you around so you know you are likely to feel good again and want to go back to your 100 mcg thyroxine.


Well, I saw the endo today - told him how bad I had been feeling on 50 of Levo and 40 of Carb. and then had my blood test. Told him I then reduced my Carb. to 20. He said that would have been his next step but he felt my blood test results were very good! Not sure what planet he's on. Listening to the patient might actually be more useful than looking at the blood tests. He is convinced I am going to submit to RAI and keeps saying so. I do, however, keep telling him I won't. Wants me to stay on 50 Levo and 20 Carb. however I feel until 5th November when I see him next!


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