Thyroid UK
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High FT4 & Low TSH - Help understanding latest Bloods

I was hoping that you lovely lot might help me interpret my latest blood tests. In November I switched from NatureThroid 1.5 grains back to 100mg of Thyroxin. I skipped 2 days a week initially for the first 4 weeks and since then have taken 100mg every day. I switched back for a few reasons including cost & raised eyebrows from friends, family & doctors. Decided to give thyroxin another try. In all honesty I feel ok but I do probably feel more tired and suffer from 'The Exhaustion" more than I did before Christmas. And I am still cold...

TSH 0.53 (0.27-4.2)

FT4 22.46 (12-22) Historically, this has always skulked around the very bottom of the range so this result has surprised me.

FT3 3.9 (3.1-6.8)

Ferritin 102.6 (13-150)

Magnesium 0.86 (0.7-1.0)

Zinc serum 12.3 (11-24)

B12 902 (191-663)

Vit D 132

I have never had my RT3 done.

I would really like my FT3 to have been higher. Do you think the low FT3 is the reason that I'm feeling cold & tired again. Just wondering if my FT3 might rise naturally as the FT4 'soaks' in? Would really appreciate any guidance about this.

4 Replies

As you say FT4 very high and FT3 very low so looks like you are t converting well. Your B12 looks good though Ferritin has room for improvement. Have you have Vit D and folate tested? They also need to be high in range to help conversion. From what you are saying I think you have been on your dose for six weeks so it's the right time to have tested so it's showing what I said so you need to get on top of the conversion. That is going to take longer but it's a work in progress so you should start on that journey. It may be that getting mineral and vitamins you won't quite be there so you may need to add some T3.


Thanks so much for your speedy reply. Yes I've has Vit D & serum folate done. They were 132 and >20 (3.9 - 26.8) respectively. Everything seems optimised from the point of view of vits & mins. Just wondering if there's anything else I can do to aid that conversion? I really would prefer not to self medicate if at all possible as that's why i've stopped buying my NDT from the USA. I just want to be straight up about what I'm taking. What are the chances of getting a doctor to prescribe T3?


Not good if you are in the U.K. Have you any bloods though from when you were on NDT? If you can show him that you were much better when you had some T3 he may look on you more kindly but don't pin your hopes in it. If you can win him over but he says not allowed to prescribe then you could always have a holiday in Greece etc and bring some back with you!



Your t4 is high as you say which may be as a result of the changes you have made.

High t4 suggests that you're not converting well to T3, which is the active hormone. I'd suggest you have an RT3 test done to see what the result says.

It seems tricky to get Endo/GP to prescribe T3 & private prescriptions are very expensive. I self medicate & my GP monitors my bloods every six months.


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