FasFasting before blood test

[Doats]

hi, following my last post, my gp has agreed to add B12, ferritin etc to my annual thyroid review.

I've been told here to not take my usual morning dose before the test;however, looking online most medical websites say its not necessary to fast.

Anyone care to clarify for me please.

thanks

[greygoose]

Fasting is more or less a sort of insurance policy because some elements in your breakfast could affect the TSH and lower it - which is not usually what you want. Cafeine, for example, will lower TSH. But doctors refuse to entertain the idea that certain things can - and will - affect blood test results. They think you can do them any old time and the results will be the same. It takes a patient to know about these things.

[tattybogle]

See the 3rd and 4th relies to this post for research supporting testing 24hrs after last dose/ and also fasting ( no breakfast) : healthunlocked.com/thyroidu.... list-of-references-

time of last dose WILL definitely a have an impact on fT4 results.

eating breakfast MAY have the effect of lowering TSH in some people, but not in others .. so just to be on the safe side, in case you are one of those people, and for consistency in case different foods have larger / smaller effects , it's wise to wait until after test to have breakfast.