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A flow sheet for the diagnosis of pernicious anemia appears in Figure 9-1. Autoantibodies to gastric parietal cells should be measured along with intrinsic factor. The demonstration of circulating intrinsic factor autoantibodies is almost diagnostic of type A gastritis and pernicious anemia (Toh et al., 1997).

FACTORS AFFECTING THE VITAMIN B12 REQUIREMENT

Aging

Plasma vitamin B12 tends to decrease and serum methylmalonic acid (MMA) concentration tends to increase with age. These changes may represent a decline in B12 status. Factors that may contribute to these changes include a decrease in gastric acidity, the presence of atrophic gastritis and of bacterial overgrowth accompanied by food-bound B12 malabsorption, severity of atrophic gastritis, compromised functional and structural integrity of the B12 binding proteins, and a lack of liver B12 stores (van Asselt et al., 1996). Percentage absorption of crystalline B12 does not appear to decrease with age (McEvoy et al., 1982). In a study of 38 healthy subjects each 76 years old taken from a larger cohort study (Nilsson-Ehle et al., 1986), cyanocobalamin absorption was found to be comparable with that reported in eight other studies of healthy younger people.

Studies of absorption in the elderly have yielded somewhat contradictory results, van Asselt and coworkers (1996) found no significant difference in cobalamin absorption (either free or protein bound) between subjects younger than 64 years (median 57) and those 65 years and older (median 75 years). These investigators could not explain the high prevalence of low cobalamin values in the elderly by either the aging process or the occurrence of mild-to-moderate atrophic gastritis. In contrast Krasinski and coworkers (1986) demonstrated that although a small proportion of the elderly with atrophic gastritis have a low serum concentration of B12 (less than 88 pmol/L [120 pg/mL]), those with lowest serum B12 values tend to have severe atrophic gastritis. Scarlett and colleagues (1992) reported a reduction in dietary B12 absorption with age that was associated with elevated serum gastrin, which indicates reduced gastric acidity.

Prevalence of Atrophic Gastritis

Large differences in the prevalence of atrophic gastritis in the elderly, ranging from approximately 10 to 30 percent, have been



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