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Thyroid UK
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T4 and T3 blood results. How do I know if I am converting properly?

I have just had my latest blood results and I think I remember someone talking about the ratio of T4 to T3 to tell if you are converting properly.

Have I remember this correctly and if so do my results show that I am or not?

TSH 2.1 (0.2-5.5)

T4 13.1 (10.0-24.5)

T3 5.0 (3.9-6.7)

These were taken at 3.40pm as I couldn't get an earlier appointment

5 Replies

I would say they don't suggest a convertion problem but a need for an increase in meds. Neither the T4 nor the T3 are even mid-range, which is much too low for you to feel well. Also your TSH is too high.

However, given that the test was done so late in the day, the TSH would have been even higher at eight o'clock, but I don't know what effect that would have had on the frees. Possibly they would have been even lower. Even so, you need an increase.

Hugs, Grey


I think I remember from a post Rod made, that ft3 and ft4 are at their lowest in the late afternoon.

I too think that you need an increase in T4. Your next blood test will then be very interesting to see xx


yup, increase :)


Mouse. Your ratio of T4:T3 is better than 3:1 which is not bad at all, no signs of conversion problem, unless when you get an increase you did not feel any better.

I agree though that they both look low so an increase would be good. Your T3 is close to OK but it all depends how you feel, of course. That is the no1 consideration.

(Just for comparison, my T4 is 24.6 (range 12-22) and my T3 is 4.5 (range 3.1 - 6.8) so my ratio is about 5.5:1 which is not a particularly good conversion rate.)

Marie XX


Thank you for this information.

I cannot increase my dose as it makes me feel worse but I think I may have a problem with my adrenals. I did a saliva test about a year ago when it was OK but I have just had Scarlet fever and since then I have had a lot of adrenal symptoms.

I have an appointment with Dr Peatfield but it is not until August.


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