Eighty-two patients who underwent gastrectomy were investigated for vitamin B12 deficiency 1 to 22 years after surgery. Serum vitamin B12 levels were found to be abnormally low in 62. Red blood cell (RBC) B12 levels were determined in 22 patients with decreased serum B12 levels, and were found to be low in 21, demonstrating a true tissue deficiency of the vitamin. More than two thirds of the patients with subnormal serum B12 levels had normal absorption by the Schilling and the plasma B12 absorption methods. It is reasoned that most such patients have difficulty in absorbing the protein-bound food B12 and not the crystalline B12 used in various B12 absorption tests. The latter therefore seem to have very little value in the follow-up of partial gastrectomy. Serum or RBC B12 determinations are suggested for this purpose, instead.
Khalid Mahmud, Donna Ripley, Alfred Doscherholmen. Vitamin B12 Absorption TestsTheir Unreliability in Postgastrectomy States. JAMA. 1971;216(7):1167–1171. doi:10.1001/jama.1971.03180330043007