Experiences with dual protein bound aqueous vitamin B12 absorption test in subjects with low serum vitamin B12 concentrations

Abstract

A dual isotope vitamin B12 absorption test in which vitamin B12 is given both in aqueous solution and bound to protein (chicken serum), was evaluated in 26 controls and 68 patients with subnormal serum vitamin B12 concentrations (19 with pernicious anemia, 13 with iron deficiency, 7 after partial gastrectomy, 7 with malabsorptive states, 5 with folate deficiency, 4 with chronic alcoholism and 13 in whom no cause was apparent). In control patients protein bound absorption decreased with age; isotope excretion was 1.0% or over in those aged under 60 and 0.5% or over in those aged 60 and above. Malabsorption of protein bound vitamin B12 with normal aqueous absorption occurred in 5 patients with iron deficiency, 3 with alcoholism, 2 after partial gastrectomy, 2 with folate deficiency and in 1 with a malabsorptive state. In alcoholics abstinence produced an improvement in protein bound absorption. All patients in the group for whom no cause could be found for the subnormal serum vitamin B12 concentration had normal aqueous absorption but 4 had malabsorption of protein bound vitamin. Although the dual isotope test gave reproducible results and was consistent with the standard Schilling test some anomalies were detected; 9 patients had reduced aqueous absorption with normal protein bound absorption. Despite this the dual test may prove useful in determining the importance of a subnormal vitamin B12 concentration where the cause is not clinically apparent. Further development is needed before it can be considered for routine use.