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Thyroid UK
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How often to repeat vitamin level testing?


Can I ask how quickly vitamin levels can change. I had good results for B12 and folate 3 years ago, and doctor is saying it doesn’t need repeating.

I have had 3 blood tests in the last 4 months and results all less than 5 but over upper limit of 4.4. So doctor has finally put me on 25mg Eltroxin.

GP has given me a 3 month prescription, but I intend going back at 6 weeks to get repeat blood test done, I need to know what might convince them to test vitD and repeat VitB12 etc too.

9 Replies

Do you know exactly what your results were, with ranges, for those tests 3 yrs ago? Just because the doctor said they were 'good' doesn't mean they were optimal. Have you been supplementing either or both?


The levels were all middle of the normal ranges. I checked the results and ranges. No supplementing by me as they were normal.

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Sorry hit reply before saying thank you for your reply.

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Would be ideal if your results were in the top quartile, rather than the middle of the range. Depends on a few factors as to whether those levels may be similar or have fallen. Absorption is important obviously, so if you are hypo you may have low stomach acid which can impair that. If I were you I'd get them tested again if possible, along with ferritin and Vit D.


Ok I will see if I can pursuade the doctor. I have only recently started having issues so I would hope that the levels are all ok still. But I will see if I can get them checked. Thank you

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Usually if vitamins are low they will go low again quite quickly if you stop or don't continue with a high enough maintenance dose


Hi thank you, I have never had any indication that any of my vitamin levels were low. Except following giving birth when slightly anemic. That is why the gp is reluctant to test them again. But I will try to push for them this time when my TSH levels are checked. (My gp is very old school type!)

Thank you


As thyroid people we tend to be low anyway but then when we are low our thyroid isn't working well so a knock on effect!


25mcg is extremely small dose. It can make you feel worse. Stick at it for 6 weeks and then get bloods tested

Push for 25mcg dose increase after this

Essential to test vitamins. They can change very quickly as you become more hypo

For full evaluation you ideally need TSH, FT4, FT3, TT4, TPO and TG antibodies, plus vitamin D, folate, ferritin and B12 tested

See if you can get full thyroid and vitamin testing from GP. Unlikely to get FT3

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 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

Link about antibodies


Link about thyroid blood tests


Print this list of symptoms off, tick all that apply and take to GP


See Box 1. Towards end of article

Some possible causes of persistent symptoms in euthyroid patients on L-T4

You will see low vitamin D, folate, ferritin and B12 listed



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