Your doctor may also order a Vitamin B12 test if you have certain nervous system symptoms. Low levels of B12 can cause numbness or tingling in the arms and legs, weakness, and loss of balance.

Other conditions under which the test may be done:

Delirium
Dementia
Dementia due to metabolic causes
Normal Results
Normal values are 200 - 900 pg/mL (picograms per milliliter).

Normal value ranges may vary slightly among different laboratories. Talk to your doctor about what your specific test results mean.

The examples above show the common measurements for results for these tests. Some laboratories use different measurements or may test different specimens.

What Abnormal Results Mean
Values of less than 200 pg/mL are a sign of a vitamin B12 deficiency. People with this deficiency are likely to have or develop symptoms. Older adults with vitamin B12 levels between 200 and 500 pg/mL may also have symptoms.

that info came from here http://www.nlm.nih.gov/medlineplus/e...cle/003705.htm