Diagnosing Cause of low B12

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    

[karajo]

Hi Heather,
An article by Wikipedia listed these causes:
1. Inadequate dietary intake of vit B12
2. Impaired absorption due to intrinsic factor deficiency caused from bariatric surgery, or celiac disease.
3. Chronic intestinal infestation of fish tapeworm.
4. Diabetes medication Metformin.
5. Hereditary causes such as severe MTHFR deficiency, homocystinuria and transcobalamin deficiency.
6. Giardiasas or similar parasite.

[pattybran]

I believe it was a blood test that diagnosed me w/ low B12.  I give myself daily 3 ml injections.  I THINK that, over time, it's helped.  Good thing about the shots is that you can drink coffee even WHILE you're shooting up.
Oooops! Just read your most recent.  I see that you already know this.

Good luck,
PattyB