Pernicious Anemia isn't JUST from Gastric Bypass, I have been living with it for over a year, and I am a carrier of Hemochromotosis (high iron in the blood - my red blood count is elevated), and I also have Thyroid Disease (Hypo).
Dealing with Pernicious Anemia is a no brainer - really, don't sweat it. My having elevated levels of iron actually cause an absorption issue with my Levothyroxin (for the thyroid). I take sublingual B12 daily, and I have to administer shots once to twice a month, depending on levels in my blood checked every three months.
For me, getting Gastric Bypass should actually lower my iron levels to a normal level (I found four case studies), and already knowing I have Pernicious Anemia, I should have little issue dealing with supplements. Knowledge is power.
Another issue folks might miss is not having enough vitamin K in their blood (I used to get bloody noses when I was pregnant, my body's way to relieve the excess blood production). I was told back then to eat a lot of parsley - no kidding! Anyhow, I am very good about taking multi viatamins, additional D, B, Calcium as well as other supplements - and I am pre-operative.
Bloodwork is fascinating business! Do some research, remember: Knowledge is Power!
B : )~