[Determination of vitamin b12 deficiency]

Development of cobalamin deficiency in the tissues is considered to be a process which lasts for years. Macrocytic anaemia and/or neurological symptoms do not occur until late in this process. Serum cobalamins as the only parameter have proved less suitable for differentiation between healthy individuals with low serum cobalamin values and patients who require cobalamin for the remainder of their lives. The need for a better indicator for cobalamin deficiency has been emphasized. Recently developed methods of measurement have rendered determinations of serum methylmalonic acid possible. This value is raised in cases of cobalamin deficiency in the tissues. The serum methylmalonic values have proved both sensitive and specific to determine the extent to which genuine cobalamin deficiency is present or not and may also be employed for monitoring the effect of treatment as the raised values becomes normalized following substitution therapy with vitamin B12.