I am wondering if there is a protocol for diagnosing the cause when someone has low B12. Ive had problems with tingling, numbness etc and my doctor decided to test my blood. It came back with low B12, 130. I have had B12 injections, quite a lot to begin with now every 3 month. Just before I was due my last injection my level was taken and was 200. They say antibodies they check for intrinsic factor are negative so no pernicious anaemia. Is the testing accurate once B12 inj has been started? I just need to know what other tests they can do to find out why it is low when my diet it great. Many thanks