Thyroid UK

Still confused/concerned after seeing endo

So I saw an endocrinologist and explained my concerns about my t4 8.0 (7.5-22.0) and tsh 0.3 (0.3-5.0) reading whilst on levo 125mg. He did all the tests to see if it's a pituitary problem and they've all come back normal apart from oestrogen which is low (strange as I have an implant and that that increased oestrogen). Since being on ndt by t4 is 10.5 and my t3 is 5.5 which is says is top of the range (5.7)

So I said well maybe my t4 was so low previously cause I wasn't taking enough and he said yes.

However that doesn't really explain why my tsh was so low too and not calling for more t4.

He wants to prescribe me t4/t3 combo rather then ndt and will check my oestrogen again at a later date.

Am I right to be concerned about the feedback loop or does it even matter as long as I'm being treated?



5 Replies

The hypothalamus monitors T4 and T3 in the bloodstream/brain (I think), and if more T4 and T3 is needed it sends out higher levels of something called Thyroglobulin Releasing Hormone (TRH). The pituitary monitors the levels of TRH in the blood and if the levels rise, more TSH is produced. And the thyroid, of course, reacts to TSH and produces T4 and some T3 in response. When the levels of T4 and T3 go up, the hypothalamus reduces output of TRH and so the loop goes on.

Problems with the thyroid cause primary hypothyroidism.

Problems with the pituitary cause secondary or central hypothyroidism.

Problems with the hypothalamus cause tertiary hypothyroidism.

Perhaps you have tertiary hypothyroidism? I'm having a logic-free day today (which is how brain fog usually affects me) and I simply cannot work out if tertiary hypothyroidism would explain your test results or not. But it might be something for you to think about.


Renee, TSH isn't a good guide to T4 and T3 levels. If TSH was low and FT4 low you weren't on sufficient Levothyroxine. On Levothyroxine FT4 should be towards the top quadrant of range.

It's different on NDT because of the T3 content. TSH is usually low/suppressed and FT4 may be low, sometimes below range, and FT3 in or towards the top third of range. Your FT4 and FT3 look good and you appear to be optimally medicated on your current dose. I'm not sure why your endo wants to switch you to synthetic T4+T3 combination.

I don't think there's anything wrong with your feedback loop in relation to thyroid and pituitary dysfunction has been ruled out. Some people have low/suppressed TSH on 75mcg Levothyroxine. Your FT4 and FT3 are good and they're what count.

It's possible there is some pituitary or hypothyalmic dysfunction affecting your sex hormes and this may be why oestrogen is low.


But wouldn't my tsh be calling for more ft4 if it's low? Even on ndt 10 is still the lower end. I told him I started on ndt because my GP refused to increase my t4 cause I was within range but I couldn't get out of bed! On 3.5 grains of ndt I can at least do that altgough I don't feel optimal


Reneey, Pituitary gland increases TSH in response to low circulating T4 and T3. TSH is shut off when sufficient T4 and T3 is detected. Your FT4 level 10.5 isn't low for someone on NDT or T4+T3 combination but it would be considered low for someone on Levothyroxine only. If more T4 was produced it would convert to T3. Your T3 is top of the range so there is no need for TSH stimulation.

You should ask your GP to test ferritin, vitamin D, B12 and folate which are often low/deficient in hypothyroid patients. Symptoms include musculoskeletal pain, fatigue and low mood which are similar to hypothyroid symptoms.


Ok so when I was on levo only 8.0 was low but on ndt 10.5 is ok.

I get b12 injections and take supplements for the rest.

Thanks Will see what happens next


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