There is another B12 evaluation test called MMA. This will be high if B12 is not working for you.

Yes, acid blocking drugs will reduce B12 absorption. They also affect Folic acid, magnesium, calcium, iron, and zinc (that we know of currently). Therefore these acid blocking drugs are implicated now in osteopenia (younger patients) and osteoporosis (older patients).
This article gives further information, and lists more minerals than I have seen so far:
http://www.nutritionreview.org/library/gastric.acid.php

If you don't use methylcobalamin, and are one of those who have genetic errors, in methylation chemistry, you may test high because of the supplements, but the B12 cyano form, will not be active in the MMA cycle. So the MMA would test high (building up) in this case. This is a common mutation, 10-30% of people have it. A doctor came on here a couple of years ago and suggested the 30% is likely. I used to post 10% only until his suggestion.

There are also tests for INTRAcellular nutrient levels. These are done by special labs... like Spectracell. Testing only the serum, which is more common by traditional doctors, is thought to be quite imperfect, since it does not show what is happening in the cells themselves.

http://www.spectracell.com/
Most integrative doctors and naturopaths, use this type of testing.