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)
- reduced iron absorption > iron defiency
- decreased release of vitamin B12 bound in the diet > contributes to vitamin B12 deficiency
- Mohamed M et al. Pernicious anaemia. BMJ 2020;369:m1319.
- NHS Wiltshire CCG. Investigation and treatment of Vitamin B12 (cobalamin) deficiency in primary care
- Royal United Hospital Bath NHS Trust. Guidelines for the Investigation & Management of vitamin B12 deficiency (accessed 25/4/2020).