In 99.5 % of labs I have noted that lower limit of normal for vitamin B 12 is set at 180 - 220 pg / ml. But I have noted patients having vitamin B 12 between this lower limit and 400 pg / ml having hyperhomocysteinemia ( and no renal failure ). Also, according to some authorities a vitamin B 12 level between 180 - 220 pg / ml and 400 pg / ml should be considered borderline deficiency.
Hypersegmented neutrophils are considered to be the first abnormality to be found on peripheral smear in Vitamin B 12 deficiency and I have noted their presence in vitamin B 12 levels between 180 - 220 pg / ml and 400 pg / ml. Shouldn't vitamin B 12 lower limits be reset to 400 pg / ml.
