I would address your B12 and Iron levels to bring them up to a mid-normal range instead of a low normal range.
A B12 level of 276 is low enough to cause problems and should be addressed. Are you a vegetarian? Or do you have digestive issues which can impair the absorption of nutrients from your food. Many doctors do not keep current on the latest nutritional recommendations. Many European and Japanese doctors have a higher lower range of 500. If you read through this B12 paper, you'll see that 50% of those with low normal B12 are actually B12 deficient and that the B12 serum test currently done, missed them.
http://www.aafp.org/afp/2003/0301/p979.html
You may want to have your copper, zinc, folate and B6 tested also. If your low in iron and B12, there a good chance you could be low in others. There are optimal ranges for nutrients.
B12 is easy to replace orally with sub-lingual tablets. There are a few forms of B12 and the most common is the cyno form. That form needs to be converted into a usable form. So, it's best to use the "methly" form of B12.
I would address the nutrients before undergoing a BMB.