Time before testing after B12 supplement

I am feeling unwell so am going for blood tests this Saturday morning. B12 is one of the tests. However I received a B12 infusion by IV drip last night (Thursday) because I was unwell and suffering fatigue and migraine. How long should I leave it before the blood tests. How long does B12 stay in the system. I was thinking of having the blood tests this Saturday morning, 36 hours after the B12 drip infusion. Please let me know any ideas or antone's experiences.

8 Replies

  • That is not enough time - that test will be a waste of time - unless you want an inflated result ! Post this on the PAS forum to double check - I am not an expert :-)

  • Thank you Marz

  • Adam, there's no point in testing B12 after an infusion. Levels should be sky high. It takes around 4 months for red blood cells to die off and renew if you want a baseline B12 test.

  • Thank you Clutter. Will it be ok to test for everything else eg TSH FT3 FT4, antibodies, vitamin D iron etc? I want an accurate baseline to see if my Levo needs adjusting as I'm feeling unwell. also I will seek appointment with the endo so need my latest results.

  • Adam, absolutely fine to do the other tests. Remember to leave 24 hours between last thyroid dose and blood draw and do an early, fasting test (except water).

  • Thank you Clutter, that's a relief, I feel I need the tests to see what's wrong

  • Adam, I hope the results help you pin down what's wrong.

  • Thank you Clutter. I appreciate your help. I had forgotten about not taking my Levi dose the night before - I take my dose in the evening - I have a blood test. Thanks for the reminder.

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