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Thyroid UK
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TSH

Hi. I take thyroxine. Does my TSH reflect levels of T4/T3 in my blood or levels of T3 in the cells of my body.

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Neither you should ask for your free T4 to be tested and your free T3. Thyroxine is a T4 drug and can convert to T3. In my experience as a patient my body didn’t convert the thyroxin to t3 so I was put on cytomel/liothyronine a t3 hormone. What is your diagnosis and have they check your feritin, vitamins D3, B12 and folate?

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Levothyroxine and liothyronine are thyroid hormone replacements and are synthetic hormones, therefore not a drug in the full sense of the word. :)

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Thyroid Stimulating Hormone is produced by the pituitary gland in the brain, when it receives signals that the thyroid hormone is not producing enough T4 and (some) T3. So it doesn't reflect the levels of thyroid hormones in the blood or cells. People who have their thyroid gland removed have suppressed levels of TSH because, obviously, there is nothing to stimulate. TSH ranges are set for healthy people, so are not good indicators if you have thyroid disease. How you feel, plus getting Free T4 and Free T3 tested are much better guages.

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where does the TSH get its signals from if it doesn't link back to the body (organs, blood, cells, etc.

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It gets feedback messages from the thyroid gland. Here is a link to a page describing the 'feedback loop'.

thyroidadvisor.com/know-thy...

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Have to disagree here... my thyroid was removed 35 years ago and I still have TSH like everybody else, as it is a pituitary hormone, not a thyroid hormone, and still keeps signalling the phantom thyroid even though there’s nobody home to get the message. But I’ve learned over the years that TSH is a totally unreliable measure of thyroid health. Even on total thyroid replacement the only thing that matters is Free t3, which correlates best with symptoms.

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I stand corrected.

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Hi fiftyone, my understanding is that TSH reflects the need for T3 and T4 as perceived by pituitary gland which releases TSH into the blood stream. Presumably the pituitary gland uses the level of circulating T3 and T4 in the bloodstream to determine the amount of TSH needed, though there could be some involvement of T3 and T4 concentations in pituitary cells.

It is the level of T3 in the cells of our body and brain that influences how we feel and there is no test for that. For some people, the levels of T3 and T4 in the bloodstream is closely related to levels in the cells of the body, but for others not. Hence the reason to adjust dose until you feel well, not until you get pretty test results.

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Probably neither. When you take thyroxine the feedback loop between thyroid-pituitary-hypothalmus is often broken (if it worked correctly on the first place)

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good point. thanks

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