Intended for healthcare professionals

Practice Easily Missed?

Pernicious anaemia

BMJ 2020; 369 doi: (Published 24 April 2020) Cite this as: BMJ 2020;369:m1319
  1. Muhajir Mohamed, consultant haematologist and associate professor of medicine1 2,
  2. Joel Thio, medical intern3,
  3. Remy Susan Thomas, medical intern4,
  4. Jehan Phillips, general practitioner5
  1. 1Department of Medicine, Launceston General Hospital, Australia
  2. 2University of Tasmania, Launceston Clinical School, Launceston, Australia
  3. 3Department of Medicine, Launceston General Hospital, Australia.
  4. 4Department of Medicine, Townsville Hospital, Townsville, Australia
  5. 5First point Healthcare, Launceston, Australia.
  1. Correspondence to: M Mohamed muhajirbm{at}

What you need to know

  • Consider pernicious anaemia in patients complaining of unexplained fatigue, memory loss, poor concentration, or paraesthesia

  • About a third of patients may have normal B12 levels and normocytic anaemia, leading to a missed or delayed diagnosis

  • Screening tests for patients with suspected pernicious anaemia should include full blood count and serum cobalamin assay

  • Prompt treatment with B12 supplementation usually reverses anaemia and neurological symptoms, and patients will require lifelong B12 supplementation

A 55 year old woman presents to her GP with fatigue, “pins and needles” sensation in her feet, and poor concentration. Clinical examination and routine blood investigations were unremarkable. Her symptoms gradually worsened over two years. She also developed exertional dyspnoea and unsteadiness while walking. On examination, she had pallor, resting tachycardia, and sensory neuropathy in both legs. A peripheral blood smear revealed macrocytic anaemia and hypersegmented neutrophils. Further investigations confirmed severe B12 deficiency secondary to pernicious anaemia.

What is pernicious anaemia?

Pernicious anaemia is an autoimmune disorder affecting the gastric mucosa with impaired absorption of dietary cobalamin (vitamin B12) resulting in B12 deficiency. Figure 1 depicts the pathophysiology of pernicious anaemia. Vitamin B12 is essential for production of blood cells and myelination of nerves. Its deficiency causes megaloblastic anaemia. Neuronal demyelination and subsequent degeneration lead to neurological and neuropsychiatric manifestations.1

Fig 1

(a) Normal process of dietary cobalamin absorption, and (b) the pathophysiology of pernicious anaemia

How common is it?

Pernicious anaemia is relatively rare. Between 50 and 200 per 100 000 people in the UK and 150 per 100 000 people in the US are affected.2 It can affect all age groups, but is seen more commonly in adults over 70 years old.1 Because of its association with autoimmune disorders such as autoimmune thyroiditis, Addison’s disease, vitiligo, and type 1 diabetes, a personal or family history of these conditions increases the likelihood of pernicious anaemia.34 …

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