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Thyroid UK
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My TSH is suddenly undetectable and T4 is high

Hello, I'm new here and I'm trying to read my way through a ton of information to make sense of what's happening to me.

I've been on levothyroxine for a good 10 years now, for Hashimotos.For most of that time 50µg worked well for me, but for a year or so things have been a lot less unstable. First my old GP decided that I needed to up my dosage slightly, so I alternated between 50 and 75µg. That worked out well for a while, then she put me back in 50µg. In september, my test results were fine.

I moved in october and my new GP tested only free T4 and TSH. The results were Serum TSH level 0.01 mu/L [0.27 - 4.2]

and Serum free T4 level 29.4 pmol/L [12.0 - 22.0]. So he halved my dosage. I was already sceptical at this point because I hadn't been feeling great. I had all the symptoms I usually have when I'm hypo. I was exhausted, constantly chilly, put on a little weight, my running performance took a massive hit, low immune system, depression etc. But they didn't want to test for anything else for a few weeks to see if the adjusment helped.

Imagine my surprise when last week's test showed that my TSH is now undetectable (<0.01mu/L) and my free T4 is even higher at 35.2 pmol/L [12.0 - 22.0]. I tried to get them to test for T3 and antibodies but they just keep saying it's unlikely, and if it was a conversion issue the TSH wouldn't be so low. But they also won't give me an alternative explanation.

They also did a full blood count and checked ferritin and glycated haemoglobin, to rule out other causes for my symptoms and everything came back normal, except for the monocyte count - 0.90 10*9/L [0.2 - 0.8]. I asked if there was a connection, but was told it's most likely a fluke.

So, my GPs solution is to not take any levothyroxine at all and wait for the next test in 6 weeks. I'm terrified of how much worse this is going to make all my symptoms. I realise that, without any of the other tests, it's really difficult to tell what's happening. But has anyone else experienced something similar?

9 Replies

Welcome to the forum, Juja.

Do you take any supplements which contain biotin?


Hello Clutter,

I have only very occasionally (5 times to be exact, counted the remaining tablets) taken Centrum Performance, which contains 40µg of Biotin. I started doing this after the first confusing test in January, though and didn't take it for at least two weeks before the recent test.



Okay, that rules out biotin interfering with the assay.

I was overmedicated with FT4 >35 and it made me feel dreadful. The best thing is to stop Levothyroxine and retest in 4-6 weeks.

Dunno why your GP thinks poor conversion can't happen with suppressed TSH. I had TSH <0.01 and FT3 was also below range but FT4 was mid-range by then.

You could order your own TSH, FT4 and FT3 hometests as your GP won't check FT3. thyroiduk.org.uk/tuk/testin... Medichecks offer #ThyroidThursday discounts.


Thank you for the link, that might be my best option. I will try to reason with my GP once more but if that doesn't work I will get a private test.


Have you had vitamin D, ferritin, folate and B12 tested?

If these are too low they can affect thyroid

Do you have Hashimoto's also called autoimmune thyroid disease, diagnosed by high thyroid antibodies? You need thyroid antibodies tested, if never done before

You really need to test FT3 as well

Private tests are available


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 money off offers.

All thyroid tests should ideally be done as early as possible in morning and fasting and don't take Levo in the 24 hours prior to test, delay and take straight after. This gives highest TSH, lowest FT4 and most consistent results. (Patient to patient tip, GP will be unaware)


Hello SlowDragon,

Yes, Hashimoto's was diagnosed a few years ago via ultrasound and blood test, but I'm not confident my GP knows much about it.

Ferritin was tested because I have a history of anaemia, but I will put folate, vitamin D and B12 on the list of things to ask for. Thank you. I have asked for T3 testing before, but was told at the time that it could not have caused the incredibly low TSH and therefore they didn't test??

I will try one last time to reason with my GP. If that doesn't work I will order a private test. Thanks for the link!

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Hashimoto's affects the gut and leads to low stomach acid and then low vitamin levels

Low vitamin levels can affect Thyroid hormone working

Poor gut function can lead leaky gut (literally holes in gut wall) this can cause food intolerances. Most common by far is gluten

According to Izabella Wentz the Thyroid Pharmacist approx 5% with Hashimoto's are coeliac, but over 80% find gluten free diet helps significantly. Either due to direct gluten intolerance (no test available) or due to leaky gut and gluten causing molecular mimicry (see Amy Myers link)

But don't be surprised that GP or endo never mention gut, gluten or low vitamins. Hashimoto's gut and gluten connection is very poorly understood

Changing to a strictly gluten free diet may help reduce symptoms, help gut heal and slowly lower TPO antibodies

Ideally ask GP for coeliac blood test first or test with a private test kit £20








Persistent low vitamins with supplements suggests coeliac disease or gluten intolerance


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If you have Hashi's, that is why your FT4 has suddenly gone high, and your TSH has therefore dropped to zero. With Hashi's, the immune system slowly destroys the thyroid, and as the cells die, they release all their stored hormone into the blood. So, your Free levels rise steeply, and your TSH drops. That's the way it works. But, it's only temporary. Eventually, all the extra hormone will be used up or excreted, and you will become hypo again - only slightly more hypo that you were before, because you have less gland. That's the way Hashi's works. And, doctors should know that, but they never do. Not even endos! It really is pathetic!

So, in six weeks time, your FT4 level will probably have dropped, and your TSH risen, and you can start all over again! But, please explain to your doctor what the problem is, so that other Hashi's patients don't get treated in the same manner. You'll be a hero! :)


Thank you so much, greygoose! That's what I thought was happening, but I guess the GP looking at me like I'm just being unreasonable and difficult when I tried discussing it made me question myself, and I didn't know exactly what the test results would look like. I will definitely try discussing it again, and this time I'll be better prepared.

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