how pernicious anaemia can be associated with atrophic gastritis - and a combined B12 and iron deficiency

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About 20% of patients with pernicious anaemia have coexisting iron deficiency - blood film may reveal normocytic anaemia, or even microcytic anaemia in extreme circumstances, masking the diagnosis of B12 deficiency (1).

A combined iron deficiency and B12 deficiency scenario may occur because of the combination of pernicious anaemia plus atrophic gastritis

  • in pernicious anaemia intrinsic factor antibodies lead a reduction in intrinsic factor and hence reduced absorption of vitamin B12
  • in atrophic gastritis antibodies to gastric parietal cells result in parietal cell damage; and hence reduced levels of intrinsic factor. There is also a consequent achlorhydria that reduces the absorption of iron; and decreases the release of dietary bound vitamin B12 - hence contributing to both deficiencies in iron and B12
Anti-Intrinsic Factor antibodies Anti-gastric parietal cell antibodies:

> lead to a reduction in intrinsic factor

> causing a reduction in vitamin B12 absorption

> causing vitamin B12 deficiency







parietal cell damage (autoimmune gastritis, atrophic gastritis) results in:

  • reduced intrinsic factor levels (and therefore contributes to vitamin B12 deficiency)

  • achlorhydria
    • reduced iron absorption > iron defiency
    • decreased release of vitamin B12 bound in the diet > contributes to vitamin B12 deficiency



  1. Mohamed M et al. Pernicious anaemia. BMJ 2020;369:m1319.
  2. NHS Wiltshire CCG. Investigation and treatment of Vitamin B12 (cobalamin) deficiency in primary care
  3. (accessed 25/4/2020)
  4. Royal United Hospital Bath NHS Trust. Guidelines for the Investigation & Management of vitamin B12 deficiency (accessed 25/4/2020).

Last edited 04/2020 and last reviewed 05/2020