How long should I leave after having my vitamin B12 injection before an intrinsic factor antibodies test? Sam Rodgers 13 July 2020 11:51 We recommend that you leave two weeks between your vitamin B12 injection and an intrinsic factor antibodies test. Related articles Why are some of your tests no longer available with finger-prick sample collection? Should I take my sample over the weekend? Have you received my sample? My test says it should be done in the morning but I work nights - what should I do? What if I can’t fill the finger prick sample tube? Comments 0 comments Article is closed for comments.