The short answer is no. Because serum vitamin B12 testing is widely available, familiar and relatively inexpensive, it has become the mainstay for assessing B12 status. It is very sensitive in severe B12 deficiency with megaloblastic anemia, but is not particularly sensitive for mild or subclinical deficiency. This is further complicated by the fact that the test has a very broad range that is considered 'normal' by most commercial laboratories. This often results in the lab reporting results that fall close to their lower limit as 'normal' when the individual is deficient. MMA (methylmalonic acid) and Hcy (homocysteine) are much more reliable markers of metabolic B12 adequacy.