pernicious anaemia

Last edited 04/2020 and last reviewed 09/2023

Pernicious anaemia (PA) is a disease of the stomach that is characterised by megaloblastic anaemia due to vitamin B12 deficiency, itself, secondary to intrinsic factor deficiency and gastric atrophy. It usually has an autoimmune basis.

PA primarily affects the elderly - most patients are over 60 years of age; less than 10% of cases are under 40 years of age; it is rare in children. Women are affected more often than men, in a ratio of 3:2.

PA affects between 50 and 200 per 100,000 people in the UK (3)

It occurs more commonly than by chance in first degree relatives, in those with blood group A and in those with fair or prematurely grey hair and blue eyes. It may be associated with autoimmune diseases, such as Addison's disease, and also with an increased risk of gastric carcinoma

  • patients with pernicious anaemia are at an increased risk of non-cardia gastric cancers and gastric carcinoid tumours
  • study evidence from analysis of 843 patients with pernicious anaemia from multiple cohort studies, 6.9% of patients (58/843) developed gastric cancer over a follow-up of 11 years (3)

Treatment is aimed at correcting the vitamin B12 deficiency.


  • about 25% of patients have neurological symptoms without anaemia and macrocytosis (3)
  • a 33% of patients with B12 deficiency may not have macrocytosis (3)


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