How long should I leave after having my vitamin B12 injection before an intrinsic factor antibodies test? Sam Rodgers 12 April 2023 15:07 Updated We recommend that you leave two weeks between your vitamin B12 injection and an intrinsic factor antibodies test. Related articles How do I activate my kit? Should I take my test whilst I have coronavirus? I take thyroid medication. Should I stop before taking my test? Do I need to fast for a cholesterol (lipids) test? Venous collection information Comments 0 comments Article is closed for comments.