The influence of serum folate on urinary excretion of vitamin B12.

It was found that in patients with decreased serum folate concentration, urinary excretion of vitamin B12 was increased in a statistically highly significant way with both oral administration of 58 Co-labeled vitamin B12 and with a 57Co-labeled vitamin B12 intrinsic factor complex. This increased vitamin B12 excretion may account for some false normal Schilling test results. Furthermore, in folate deficiency, the intrinsic factor no longer seems required for vitamin B12 to pass the intestinal wall. It is also questionable whether vitamin B12 absorbed through the intestine under these circumstances could be properly metabolized. Besides statistical evidence, some clinical support for this theory is presented. These findings offer a possible clue for some literature reports that have lacked a satisfactory explanation.