Found this as I was trawling through the internet (as we have to for information!) and found this interesting, particularly regarding the Schilling test.
Interesting link about Megaloblastic ... - Pernicious Anaemi...
Interesting link about Megaloblastic Anemia
Very good. However, it's important to remember that meagaloblastic anaemia isn't the only indicator of B12 deficiency. It's quite common to be deficient but for there to be no changes in red blood cell size (especially if one is also iron deficient). I once read somewhere that megaloblastic anaemia was inversely correlated with neurological symptoms (as the incidence of one increased the other decreased).
I very quickly realised that this is a complicated health issue! I was intrigued with this aspect as I am still suffering from breathlessness even after having all my loading doses and self supplementing for the last 4 weeks.
Seems to me you have to do lots of reading and be able to go back to the doctors armed and fully loaded with information so you can argue your case.