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Thyroid UK
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T4-T3 underconversion


After 3 weeks of detective work and a tonne of finger prick tests I have discovered that I am undercoverting T4 into T3. It's such a relief to have figured out why I have been having so many symptoms (anxiety, tired, dizzy, sweaty) but now I would LOVE some advice from people in a similar situation about kick starting my conversion again. I feel like I know why it happened (car crash, lost job, dad died hence cortisol through the roof) but now I would like to super speed my recovery a) to feel better and b) to try for a baby, which I only want to do if I am healthy.

Thanks everyone - this forum is the best and making me not feel alone 😄😄😄

11 Replies

Do you have some blood test results that indicate you are underconverting? Certain road traffic accidents such as whiplash can cause minor central hypothyroidism which would affect hormone levels and probably conversion. Conversion is also reduced by depression and this becomes a bit of a vicious circle as hypothyroidism can cause depression. It would be useful to see a few blood test results along with details of any thyroid medication.

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Hi, thanks for replying. I had no idea that whiplash could cause hypothyroidism!! I have literally never recovered from what was a fairly minor crash last March - wow!

My results are:

TSH 1.55 ug/d

FT4 1.18 ng/dl

FT3 1.15 of/ml

T4 7.1 ug/d

T3 104 ng/dl

RT3 195.3 pg/ml

Peroxidase antibody 15.5

Thyroglobulin antibody 10

Thanks for looking at these for me 😊

What do you think?



The results are largely meaningless unless you include the lab ref ranges (the figures in brackets after results).


Ok thanks for the advice.

Here are all results with ranges:

TSH range 1.8-3

me: 1.55

FT4 range 1-1.5

me: 1.18

FT3 range 3-4

me: 1.15

T4 range 6-12

me: 7.1

T3 range 100-180 me: 104

RT3 range 90-350 me: 195

Peroxidase antibody range 4 or less

me: 15.5

Thyroglobulin antibody range 4 or less

me: 10

I would be so grateful for anyone's feedback 😊


You have a very low fT3 but your TSH is not elevated. This is not normal. Whiplash can cause 'secondary hypothyroidism' which is when the pituitary fails to produce sufficient TSH (and also TSH with reduced bioactivity). You should insist on a referral to an endocrinologist to check out your pituitary function.


Thank you I will take my results to the GP 👍🏻


Hi. What are you FT4 and FT3 levels look like(with ranges)?


FT4 range 1-1.5 me: 1.55

FT3 range 3-4 me: 1.15

T3 range 100-180 me: 104

Thanks for your help ☺️

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Yeah, you seem low on T3 for sure. Those ranges are pretty narrow. I'm also trying for a baby, and a baby won't happen with low thyroid hormones, or at least, the chances are lowered by this. I have all those symptoms: dizziness, fatigue, anxiety in the mornings (always waking up as if someone jolted me up) and sweating from the minimum exertion.

I hope your nutrients are also good because if vitamins and minerals are low, there is little chance that you are converting any of the little T4 you have. I hope you find relief soon. This is not a nice way to live at all.


It's rubbish isn't it. Would just love to go back to feeling 100% healthy- I am so determined to get there. Would love to get rid of the anxiety and dizziness the most of all the symptoms. We will get better 😄

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Magenta76 happy for you that you now understand that your conversion is not efficient . You might try some nutrients that help thyroid conversion and metabolism . Selenium helps with conversions , B-12/folate , Vit"D" , Iron if needed it , magnesium . Iron if needed it and Calcium must be dosed four hours away from thyroid meds .

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