Thyroid UK
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Serum Versus Urine Test Results

Serum Versus Urine Test Results

Hi, I did these tests two days apart. Please have a look at the attached image and let me know if you think my comments make sense. I was taking 75T4 and 15T3, the serum test was taken 15 hours after last T3 dose. Interesting that serum and urine T4 levels are identical but T3 is MUCH lower in urine ( I am heterozygous DI02 )

Thank you - Andi

4 Replies

Andi, it appears you aren't getting enough T4 (75 is low even with additional T3) which means you don't have enough to make or convert into FT3. Now the bit of T3 that made it into your cellsw ill be reduced even more. Have you increased both T4 and T3 beyond what you take now?

I'll have to remind myself about the deiodenases.


I have increased dose to 100T4 and 20T3 about 3 weeks ago and I am feeling better and will wait another week or two before retesting ( both urine and serum )

Is there a translation anywhere of the articles mentioned above? Endo at Addenbrooks reckons urine test is unreliable because of the tiny amounts of hormone present in urine.


I am impressed that the TSH reading in both tests is identical. I hope this means we will end up having urine tests rather than blood tests - much quicker and less painful (depending on the nurse of course).

1 like

The urine test did not give a TSH value - I copied that over from the Serum test. The T4 levels matched exactly however.


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