Thanks for your question.
Basically they want to know the cause for your low vitamin B12, hence asking for the further tests. Or else if you meet the doctor with the present investigations the doctor will then again ask you to have the tests done. Therefore it is in your best interests to have the test done before consulting your doctor. Your doctor needs to establish the diagnosis and the cause for the vitamin B-12 deficiency for the appropriate treatment. You would have received the emergency treatment at the A and E.