Further studies on the use of serum gastrin levels in assessing the significance of low serum B12 levels.

The reported incidence of low serum vitamin B12 levels in patients ranges from 4% to 8%. In only a small percentage can this be ascribed to readily diagnosed pernicious anemia, malabsorption syndrome, or to gastrointestinal surgery. This leaves a number of patients in whom the meaning of the low serum B12 is not immediately apparent. In 71 patients with intact gastrointestinal tracts, hematological indices did not adequately separate patients with decreased absorption of unbound B12 from those with normal absorption. A low absorption of B12, either unbound or food-bound, was found, however, when the level of serum gastrin was elevated. In contrast, a normal absorption of unbound B12 was likely (95% of 44 patients) when the serum gastrin was normal.