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Pernicious Anaemia

Pernicious anaemia, also known as vitamin B12 deficiency anaemia, is a condition where insufficient red blood cells are produced due to a deficiency in vitamin B12. It primarily results from a lack of intrinsic factor, a protein essential for vitamin B12 absorption in the small intestine.

This can be due to autoimmune attacks on the stomach cells that produce intrinsic factor, surgical removal of parts of the stomach or small intestine, or inherited disorders.

Micrograph showing nodular enterochromaffin-like cell hyperplasia
Micrograph showing nodular enterochromaffin-like cell hyperplasia, as demonstrated with chromogranin A immunostaining, in the body of the stomach. Parietal cells are not readily apparent.

Signs and Symptoms

Pernicious anaemia often develops gradually, leading to insidious and unnoticed damage. Initial symptoms typically include fatigue and weakness, but can also encompass shortness of breath, dizziness, headaches, and rapid or irregular heartbeat.

Additional symptoms may include a smooth red tongue (glossitis), pale or yellow skin, easy bruising, low-grade fevers, and gastrointestinal issues such as nausea, loss of appetite, and heartburn. Neurological symptoms can also occur, including numbness or tingling in the hands and feet, difficulty walking, poor balance, muscle weakness, and cognitive impairments such as memory loss and confusion.

In severe or prolonged cases, nerve cell damage may lead to more serious complications like neuropathic pain, blurred vision, depression, and even dementia.


Vitamin B12, which cannot be produced by the human body, must be obtained from the diet. The absorption of B12 requires intrinsic factor produced by the stomach's parietal cells. Pernicious anaemia is commonly caused by an autoimmune response against these cells, leading to a deficiency in intrinsic factor.

Other causes include surgical removal of parts of the stomach or small intestine, and chronic conditions such as celiac disease, Crohn's disease, and infections like Helicobacter pylori.

Atrophic gastritis showing patchy atrophy of oxyntic mucosa
Atrophic gastritis showing patchy atrophy of oxyntic mucosa


The body stores several years' worth of B12 in the liver, but chronic autoimmune activity can lead to B12 depletion and resultant anaemia. B12 is very important for DNA synthesis and neurological function. Its deficiency leads to the accumulation of methylmalonyl-CoA and levomefolic acid, disrupting DNA replication and causing the formation of large, fragile red blood cells (megaloblasts).

Neurological symptoms arise due to the accumulation of methylmalonyl-CoA, which interferes with nerve function.


Pernicious anaemia is diagnosed through blood tests showing megaloblastic anaemia and elevated mean corpuscular volume (MCV) with normal mean corpuscular haemoglobin concentration (MCHC). The presence of hypersegmented neutrophils on a blood smear is pathognomonic.

Serum B12 levels help detect deficiency but do not determine the cause. Additional tests include checking for antibodies to intrinsic factor and parietal cells, measuring levels of methylmalonic acid (MMA) and homocysteine, and evaluating gastrin levels. A gastroscopy with biopsy can confirm atrophic gastritis, often associated with pernicious anaemia.

Immunofluorescence staining pattern of gastric parietal cell antibodies
Immunofluorescence staining pattern of gastric parietal cell antibodies on a stomach section


Treatment involves vitamin B12 supplementation, typically through intramuscular injections. Initially, high daily doses are administered, followed by less frequent dosing as the condition stabilises. Oral B12 supplements may be effective, but there is insufficient evidence to support their efficacy in all cases.

Lifelong treatment is usually required. Folate supplementation should be monitored to avoid masking B12 deficiency. In severe cases, blood transfusions may be necessary.

Hydroxocobalamin injection
Hydroxocobalamin injection usp (1000 mcg/ml) is a clear red liquid solution of hydroxocobalamin available in a 30-ml brown glass multidose vial.


With appropriate treatment, individuals with pernicious anaemia can lead healthy lives. However, untreated pernicious anaemia can lead to irreversible neurological damage, excessive fatigue, and other complications. There is also an increased risk of gastric cancer associated with the atrophic gastritis commonly seen in pernicious anaemia.


Pernicious anaemia affects about 0.1% of the general population and 1.9% of people over 60 years old. It is more prevalent in Northern Europe and among people of African descent. Improved diagnostic tools and increased awareness have contributed to higher reported incidence rates.


The condition was first described in 1824, with significant advances in understanding and treatment occurring in the early 20th century. The discovery of the importance of liver in haematopoiesis and the isolation of vitamin B12 were central milestones.

1930 advert for liver extract to treat pernicious anaemia
1930 advert for liver extract to treat pernicious anaemia

Self-assessment MCQs (single best answer)

What is the primary cause of pernicious anaemia?

Which of the following is NOT a symptom of pernicious anaemia?

What type of cells are primarily attacked in the autoimmune response causing pernicious anaemia?

Which substance is essential for the absorption of vitamin B12 in the small intestine?

What is the pathognomonic feature seen in the blood smear of a patient with pernicious anaemia?

Which test can confirm the presence of atrophic gastritis associated with pernicious anaemia?

What is the primary treatment for pernicious anaemia?

Which form of vitamin B12 is commonly used in intramuscular injections for treating pernicious anaemia?

What is a potential long-term complication of untreated pernicious anaemia?

Roughly what percentage of people over 60 years old are affected by pernicious anaemia?


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