Biomarkers of B12 status reported in the cases included serum B12 level, mean corpuscular volume (MCV), and serum homocysteine. Serum methylmalonic acid (MMA) is an additional biomarker of B12 status; however, it was not widely reported in the cases reviewed. Serum B12 level was reported in all but two cases [8,16]. MCV levels were reported in 53 cases and serum homocysteine levels in 13 cases.