Thyroid UK
84,259 members99,285 posts

Blood tests

Hi all

I'm having tests tomorrow for vitamin levels and thyroid function having been taking levothyroxine for two weeks. Just wonder if there is anything I should do or not do before the test? Should I take my levothyroxine pill in the morning as usual or not?

I realise 2 weeks is quite soon for a retest of thyroid function but I'm feeling peculiar on levothyroxine so want to stop if for a while to see if the strange symptoms stop. Dr advised a retest of thyroid function before I stop it.


11 Replies

Leave off Levo for 24 hours, so if you took your Levo this morning, take tomorrow morning's dose after the blood draw. Also, fast overnight (you can have water) and do the test before 9am, earlier of possible.

If you're taking any vitamin or mineral supplements, don't take them before the test, take them afterwards.


I don't think it's a very good idea to stop levothyroxine and I believe you should continue for six weeks before you have a blood test. The reason being that it is slow to build up and that's why six weeks is advisable.

It is a bit unusual for doctor to advise a blood test before stopping levothyroxine, the reason is that hypothyroidism is classed as a serious disease of the thyroid gland and a patient, so diagnosed, will not pay for any other mediations for their lifetime due to the seriousness of hypothyroidism.

Anyway, a blood test should be taken at the very earliest, fasting, and allow a gap of 24 hours between last dose of levothyroxine and the test and take afterwards. (not if you're going to stop it). I shall also give you a list of clinical symptoms of hypothyroidism. Has your doctor checked you for thyroid antibodies, if you do have them you have an Autoimmune Thyroid Disease called Hashimoto's but the treatment is the same. It's just that the antibodies attack the thyroid gland until it cannot produce any thyroid hormones whatsoever which keeps your body working from head to toe.

1 like

Thanks Shaws. Yes I am in two minds about stopping the levo but I am so desperate to know if the vertigo and neurological symptoms I am having is due to the medication. Ive been really anxious that there is something terribly wrong with me.

When I say Dr I mean consultant endocrinologist.... He said ok to stop briefly to see if symptoms improve. He didn't need overly concerned as he said I was only borderline hypo and only suggest starting treatment to prepare for future pregnancy.

I do have hashimotos although this is self diagnosed and not officially yet by Dr.


Hashimoto's is the commonest form of hypothyroidism. It is the antibodies in it which attack our thyroid gland until we become hypothyroid. Treatment should be started if you have antibodies and it is the same as hypothyroidism.

You could try and take one anti-histamine tablet 1 hour before you take levo and it may prevent the problems you have. If it does there's something in the fillers/binders which could be affecting you so you'd have to ask pharmacist for another make of levo with different fillers/binders.

If you are hoping to become pregnant, yes, it is necessary for you to have good thyroid hormones. Some people miscarry due to hypo.

1 like

Thanks that's interesting about the anti histamines. I'll definitely ask the pharmacist about that


Neurological symtoms and dizziness can be caused by hypothyroidism. I have had them for ages before my bloods caught up and went out of range (along with lots of other symptoms. . I have been taking levo for just over two weeks and have seen an improvement in last couple of days.

Are you taking any b vitamins. I was caught out a few weeks ago as I didn't stop my b supplement and it altered my TSH and T4 test I had. Luckily my GP agreed to retest so we are clear or off that the b complex affected the result. Any supplements containing biotin should by stopped 4/5 days before thyroid testing.

As a precaution, I now stop all b vitamins a week before and my other suppements 3-5 days before as I can't cope with the leg cramps when I'm not taking magnesium for too long.

Will add a reminder to my diary for also stopping levo on the morning of these test.

If you've been taking biotin I would dmstingly recommend rearranging the test for he end of the week at least to give time for it to be out of your system. I was taking low dises and it brought all my results in range (when they weren't). At higher doses people have been misdiagnosed with graves. Or presumbabkg had medication adjusted based on false results.


How would you describe be your vertigo and what Neuro symptom have you been getting?


Thanks Minimum. The vertigo is like a fogginess round my head. Not too bad when I'm sitting down. When walking it feels like I'm on a boat -just a slight feeling of things around me being wonky and unstable. Ive had three eye tests recently and all of so don't think it's my eyes.

Other symptoms are internal vibrations in my back and legs when resting a bit of numbness in hands and feet but this has gone now. Also muscle weakness like I can't use my legs and arms fully although I can ( it just feels like I can't).

I am also open to the idea that these symptoms could be due to anxiety as when the gp mentioned the diagnosis and was worried about antibody levels I went into panic mode and really stressed myself out worrying about hashimotos etc. I am as well susceptible to health anxiety and I know that can make symptoms worse.


That almost exactly describes the symptoms I have been having which I fully expect to be my hypothyroidism. Have been on medication for just over two weeks and it's early days but symptoms seem to be subsiding including the dizziness, tingling/skin crawling, weakness on arms and legs and numbness.


That's interesting and reassuring that it is down to the condition. Did you have your symptoms before you started the levo or after you started?


For months before I was diagnosed and started levo.


You may also like...