For garden-variety B12 deficiency, due to inadequate intake from food or supplements, oral supplementation suffices to fix the problem. But pernicious anemia cannot be treated with oral B12, because the lack of intrinsic factor will prevent absorption. The appropriate treatment is B12 injections your doctor must provide. In some cases, genetic mutations can limit the ability to metabolize B12 as well, in which case you will need to get the active form, called methylcobalamin, instead of the more common cyanocobalamin.
Health-care professionals are, of course, taught to be on the lookout for B12 deficiency, particularly in patients over age 50 with suggestive signs or symptoms. But health care is at its best when both clinician and patient are on the ball! I encourage an empowered, assertive role for all patients.
If you are at all concerned about the possibility of B12 deficiency in yourself, or a loved one, ask … before you forget the question!