Just had first blood results after replacing Levothyroxine with NDT.
T3- 8.0
T4- 16.7
TSH-0.01
GP is concerned about TSH level being very low.
Feel better than I have for years. GP wants me to lower dose and retest in two months.
What is causing such low TSH? Is it dangerous? Is there something else I can do other than cut dose of NDT?
Sorry, but we need the ranges for those results. Ranges vary from lab to lab, so we need the ranges from the lab where your blood was tested.
No, low TSH is not in any way dangerous. If you're taking a decent amount of T3, it is going to be suppressed because you don't need it anymore. The pituitary produces TSH to stimulate the thyroid to make more hormone, when it senses that there's not enough circulating thyroid hormone in the blood. When it senses that there is enough, it stops producing TSH. TSH only affects the thyroid and thyroid hormones. So, your doctor is wrong to be worried about it.
On the other hand, that FT3 looks like it might be over-range, which might mean that you're over-medicated. How do you feel on that dose? If you feel that you might be over-medicated then it would be a good idea to try reducing your NDT slightly. But, it's doubtful that that would raise the TSH. You'd have to raise it a lot to do that, making yourself hypo in the process. So, don't worry about the TSH. It's the FT3 the most important number. 
Range
T3 8.0 3.1- 6.8
TSH 0.01 0.27- 4.2
I feel good but need to read up on what too much would feel like.
On 2 tablets daily. Would it be sensible to reduce by 1/4 rather than 1/2 tablet?
Oh, definitely reduce by 1/4 grain, never more than that at a time.
If you were over-medicated, you might not feel anything untoward. Or, you might have hyper-like symptoms. But, the thing is, some people have varying degrees of thyroid hormone resistance, where the levels in the blood look good - or too much - but it's not getting into the cells. These people need higher doses.
Recommended on here that all thyroid blood tests should ideally be done as early as possible in morning and fasting.
If/when also on T3, or on NDT make sure to take last dose 8-12 hours prior to test
Is this how you did your test?
You need vitamin D, folate, ferritin and B12 tested too
Do you have autoimmune thyroid disease also called Hashimoto's ? Diagnosed by high thyroid antibodies.
For full Thyroid evaluation you need TSH, FT4 and FT3 plus both TPO and TG thyroid antibodies tested. Also extremely important to test vitamin D, folate, ferritin and B12
Low vitamin levels are extremely common, especially if Thyroid antibodies are raised
Private tests are available. Thousands on here forced to do this as NHS often refuses to test FT3 or antibodies or vitamins
thyroiduk.org.uk/tuk/testin...
Medichecks Thyroid plus ultra vitamin or Blue Horizon Thyroid plus eleven are the most popular choice. DIY finger prick test or option to pay extra for private blood draw. Both companies often have special offers, Medichecks usually have offers on Thursdays, Blue Horizon its more random
What TSH level is too low on NDT + low sodium 
On NDT and my TSH in a range
Low TSH & T4, with a high T3. Help with NDT dosage plse
High TSH on high NDT dose
Low TSH and carnivore diet
