Yes but someone probably needs to request it specifically. My first thought was that he should try B-12 shots as well, they are cheap, their effects are nearly instantaneous, and you can take shitloads of it without any problems. Unfortunately they are prescription only in the US, you can get them OTC in Mexico.
"and the other main diagnostic signpost of low levels of serum B12 cannot be relied upon, as sufferers can have high levels of serum B12 and still have pernicious anemia."
It's really hard to diagnose, there are no reliable tests for it.
It should. I've known a few people that inhaled Nitrous recreationally (which is known for depleting B12 very rapidly); it was a common side effect (other than it being an anxiolytic) that you would lose sensation in your outer extremities. People that do too much can do serious damage to the body, similar to the symptoms listed by the OP and the root commenter.
