what can b12 injections do for you How Quickly Does Shot Work? Does It Help to Lose Weight? The B12 Shot: What Every
Description
If your test is negative it means we can review the need for the injections and it is likely that you do not need more

BMJ 1 , 16451648 (1977)

Here, the bodys ability to absorb B12 is fine

Also - all the guidelines state that once B12 therapy has commenced, B12 serum levels are meaningless in terms of evaluating clinical efficacy (as you say, they'll always be high because of the injections)