Flowchart makes it clear that in UK, people who are symptomatic for B12 deficiency should have an IFA (Intrinsic Factor Antibody) test and start initial b12 treatment. This applies whether B12 is low or within range.
IFA test is not always reliable and it is possible to still have PA (Pernicious Anaemia) even if IFA test result is negative (called Antibody Negative Pernicious Anaemia).
7) Book "What You Need to Know About Pernicious Anaemia and Vitamin B12 Deficiency" by Martyn Hooper. Book is up to date with UK B12 guidelines. He has written two other books about PA and B12 deficiency.
I found "Living with Pernicious Anaemia and Vitamin B12 Deficiency " helpful as well due to case histories in it.
8) Book "Could it Be b12:An Epidemic of Misdiagnoses" by Sally Pacholok and JJ. Stuart (USA authors)
Very comprehensive book about B12 deficiency and lots of case histories.
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