pernicious anemia

  My 58 y.o. mother has been diagnosed with pernicious anemia for 3 years, taking monthly B12 shot and daily flic acid tablets.  She had been doing great until recently, fatigues half way through the month between shots.  Her recent bloodwork showed a slight decrease in WBC;s, slight increase in the size of her RBC's and the hematologist told her the B12 isn't staying absorbed as well.  He is stumped,according to my mother, and mentioned the possibility of a bone marrow test.  What would they be checking for, and why aren't the B12 shots stabilizing her anymore.  What else could be wrong?
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Vitamin B12 deficiency can cause neurologic problems, and as such we have some experience with it. However, when it comes to figuring out exactly why someone has a vitamin B12 deficiency or how the vitamin B12 is affecting components of blood (macrocytic anemia, etc), we send people to hematologists.
Your questions are best answered by a hematologist. Sounds like you've seen one. If yours is stumped, he may do a bone marrow biopsy, but I'm getting out of my league here.
If you want general education about B12 etc, such as what we provide here about neurologic disease, you might try to see if there is a general medicine or hematology forum. I haven't looked around or I'd give you a specific web address. I hope this helps. CCF MD mdf.