Pernicious anaemia and B12 deficiency

What is pernicious anaemia?¹

Pernicious anaemia is an autoimmune gastritis that causes atrophy of all layers of both the body and fundus of the stomach, and loss of normal gastric glands, mucosal architecture, and parietal and chief cells, leading to atrophic gastritis. This atrophy reduces the number of parietal cells which secrete intrinsic factor (IF).

• IF is essential for the absorption of vitamin B12. Antibodies to IF are very specific for pernicious anaemia, but only present in 50% to 70% of people with the condition.

• Anti-parietal cell antibodies occur in 90% of people with pernicious anaemia, but they are less specific and common in older people (16% of women aged over 60 years) who do not have pernicious anaemia.

The resultant malabsorption of vitamin B12 leads to vitamin B12 deficiency, which ultimately leads to pernicious anaemia.

Autoimmune gastritis is a microscopic disease because patients present with no or vague symptoms, and endoscopic changes are very uncommon. Autoimmune gastritis only becomes a clinical disease when pathologists diagnose it in gastric biopsies performed for a variety of clinical indications.²

Vitamin B12 (cobalamin) is present in meat and animal protein foods. Absorption occurs in the terminal ileum and requires intrinsic factor (IF), a secretion of gastric mucosal (parietal) cells, for transport across the intestinal mucosa. Body stores of vitamin B12 are in the region of 2-3 mg, which is sufficient to last for 2-4 years.

Causes of pernicious anaemia (Aetiology)²

Normally, the parietal cells produce hydrochloric acid and intrinsic factor. Gastrin production by the G cells is regulated by acid in the antrum. Hence, low antral acid stimulates gastrin production, whereas high antral acid decreases production of gastrin.

Autoimmune gastritis is a chronic autoimmune gastritis in which CD4+ T cells target parietal cells. This leads to both parietal cell and chief cell loss with eventual atrophy of the mucosa. The loss of parietal cells creates a state of constant achlorhydria, causing antral G cells to continuously produce gastrin. Therefore, the reduction in parietal cells leads to hypergastrinaemia. Complete loss of parietal cells leads to a lack of intrinsic factor production that, if severe enough, may result in pernicious anaemia. Gastric acid is also required for the absorption of inorganic iron, so patients with autoimmune gastritis can also present with iron deficiency.

Causes of vitamin B12 deficiency¹

Causes of vitamin B12 deficiency include:

• Gastric causes: gastrectomy, gastric resection, atrophic gastritis, Helicobacter pylori (H. pylori) infection or congenital IF deficiency or abnormality.

• Inadequate dietary intake of vitamin B12 - eg, a vegan diet.

• Intestinal causes - eg, malabsorption, ileal resection, Crohn's disease affecting the ileum, chronic tropical sprue, HIV and any radiotherapy causing irradiation of the ileum.

• Drugs - eg, colchicine, neomycin, metformin, anticonvulsants.

• Long-term use of drugs that affect gastric acid production (eg, H₂-receptor antagonists, proton pump inhibitors) can worsen deficiency because gastric acid is needed to release vitamin B12 bound to proteins in food.

• Recreational nitrous oxide use. Recreational nitrous oxide is a relatively common cause of subacute combined degeneration of the cord in young people. Recreational use of nitrous oxide has increased rapidly in recent years and is now the second most commonly used recreational drug among young people in the UK.³

Common risk factors for vitamin B12 deficiency include:⁴

• Diet low in vitamin B12 (without the regular use of over-the-counter preparations), for example, in people who:

  • Follow a diet that excludes, or is low in, animal-source foods (such as a vegan diet, or diets excluding meat for religious beliefs).

  • Do not consume food or drinks fortified with vitamin B12.

  • Have an allergy to some foods such as eggs, milk or fish.

  • Find it difficult to buy or prepare food (eg, people who have dementia or frailty, or those with mental health conditions).

  • Find it difficult to obtain or afford foods rich in vitamin B12 (eg, people on low income).

  • Have a restricted diet (eg, because of an eating disorder).

• Family history of vitamin B12 deficiency or an autoimmune condition.

• Atrophic gastritis affecting the gastric body.

• Coeliac disease or another autoimmune condition (such as thyroid disease, Sjögren's syndrome or type 1 diabetes).

• Medicines: colchicine, H2-receptor antagonists, metformin, phenobarbital, pregabalin, primidone, proton pump inhibitors, topiramate.

• Previous abdominal or pelvic radiotherapy.

• Previous gastrointestinal surgery: many bariatric operations (eg, Roux-en-Y gastric bypass or sleeve gastrectomy); gastrectomy or terminal ileal resection. Vitamin B12 deficiency is very likely in people after total gastrectomy or complete terminal ileal resection, if they are not receiving either oral or intramuscular vitamin B12 replacement.

How common is pernicious anaemia? (Epidemiology)¹

• The prevalence of pernicious anaemia varies geographically but overall has been estimated at 0.1% in the general population and 1.9% in those aged 60 years and over.

• Adult pernicious anaemia (the most common cause of B12 deficiency and megaloblastic anaemia) occurs most commonly in people aged 40–70 years, with a mean age of onset of 60 years among white people. In black people the mean age is 50 years, with a bimodal distribution due to an increased occurrence in young black females.

• Pernicious anaemia accounts for 80% of cases of megaloblastic anaemia due to impaired absorption of vitamin B12.

• Pernicious anaemia affects more women than men, with a ratio of 1.6:1, and a peak occurrence in those aged 60 years.

How common is vitamin B12 deficiency?

• There are currently no accurate prevalence figures for B12 deficiency anaemia in the UK. Data from USA and Netherlands indicates that it affects at least 3% of those aged 20–39 years old, 4% of those aged 40–59 years, 6% of those 60 years or over, and over 20% aged 85 and older.

• Marginal depletion affects 15% of those aged 20–59 years old and more than 20% of those aged 60 years or over.

• For people with vegan diets, around 11% are deficient in vitamin B12.

Symptoms of pernicious anaemia (presentation)¹⁴

Autoimmune gastritis presents with no or vague symptoms, and only becomes a clinical disease when diagnosed in gastric biopsies performed for a variety of clinical indications. Therefore the presentation of pernicious anaemia is much more often that of vitamin B12 deficiency and anaemia, rather than gastrointestinal symptoms.²

The symptoms and signs of vitamin B12 deficiency are variable and often non-specific. The diagnosis of vitamin B12 deficiency should not be excluded solely on the absence of either anaemia or macrocytosis. Vitamin B12 deficiency can be associated with mental health problems, including symptoms of depression, anxiety or psychosis.

Common symptoms and signs of vitamin B12 deficiency include:

• Abnormal findings on a blood count such as anaemia or macrocytosis.

• Cognitive difficulties such as difficulty concentrating or short-term memory loss (sometimes described as 'brain fog'), which can also be symptoms of delirium or dementia.

• Eyesight problems related to optic nerve dysfunction: blurred vision, optic atrophy, visual field loss (scotoma).

• Glossitis.

• Neurological or mobility problems related to peripheral neuropathy, or to central nervous system disease including myelopathy (spinal cord disease): balance issues and falls caused by impaired proprioception (the ability to sense movement, action and location) and linked to sensory ataxia (which may have been caused by spinal cord damage), impaired gait, pins and needles or numbness (paraesthesia).

• Symptoms or signs of anaemia that suggest iron treatment is not working properly during pregnancy or breastfeeding.

• Unexplained fatigue.

Findings on examination may include pallor, heart failure (if anaemia is severe), lemon tinge to the skin, glossitis and oral ulceration. Neuropsychiatric features may include irritability, depression, psychosis and dementia. Neurological features may include subacute combined degeneration of the spinal cord and peripheral neuropathy.

• Peripheral loss of vibratory sense and position are early indications of central nervous system (CNS) involvement, accompanied by reflex loss and mild-to-moderate weakness. Later stages may be characterised by spasticity, Babinski's responses and ataxia.

• Other uncommon neurological symptoms include impairment of pain, temperature and touch sensations. The legs and feet are involved earlier and more consistently than the hands.

• Yellow-blue colour blindness may occur.

• Psychiatric symptoms (usually more prominent in advanced cases) may include depression, paranoia (megaloblastic madness), delirium, confusion and dementia.

• Severely anaemic patients may present with heart failure, often triggered by an infection. Hepatomegaly and splenomegaly may be present.

Differential diagnosis¹

Causes of megaloblastic anaemia

• Folate deficiency - poor diet, goat's milk, gluten-induced enteropathy, tropical sprue, pregnancy, prematurity, chronic haemolytic anaemias (eg, sickle cell anaemia), malignant disease, increased renal loss (congestive cardiac failure, dialysis), drugs (anticonvulsants, sulfasalazine).

• Neurological complications such as subacute combined degeneration of the spinal cord may occur despite normal serum B12 levels. For example, failure of intracellular transport of B12 by transcobalamin-2 can lead to functional B12 deficiency but with apparently normal serum levels.⁵

Causes of macrocytosis

• Pregnancy and the neonatal period.

• Alcohol excess.

• Liver disease.

• Severe hypothyroidism.

• Reticulocytosis (eg, post-acute blood loss or haemolytic anaemia).

• Other blood disorders - red-cell aplasia, aplastic anaemia, myeloid leukaemia, myelodysplastic disorders.

• Changes in plasma proteins (eg, increased paraprotein secondary to multiple myeloma) may cause a spurious rise in mean cell volume (MCV) without the presence of macrocytes.

• Drugs that affect DNA synthesis - eg, azathioprine, hydroxyurea.

Investigations^{1 6}

Offer an initial diagnostic test for vitamin B12 deficiency to people who have:

• At least 1 common symptom or sign (see above), and

• At least 1 common risk factor for the condition (see above).

Use clinical judgement when deciding whether to test people who have at least 1 common symptom or sign but no common risk factor.

Initial tests

• Use either total B12 (serum cobalamin) or active B12 (serum holotranscobalamin) as the initial test for unless:

  • Use active B12 as the initial test for suspected vitamin B12 deficiency during pregnancy.

  • If suspected vitamin B12 deficiency caused by recreational use of nitrous oxide, use plasma homocysteine or serum methylmalonic acid (MMA); if using plasma homocysteine, refer to phlebotomy services in secondary care for this test.

• Take blood samples for diagnostic tests before starting vitamin B12 replacement.

• Do not delay vitamin B12 replacement while waiting for the test results of people with suspected megaloblastic anaemia and neurological symptoms, especially symptoms related to sub-acute combined degeneration of the spinal cord.

• Consider starting vitamin B12 replacement while waiting for the test results of people with suspected vitamin B12 deficiency that is a side effect of taking medicine.

Interpreting total or active B12 test results

Use the following thresholds to guide diagnosis or where there is substantial local variation in total B12 validated thresholds, use those set by the laboratory doing the testing.

• Confirmed vitamin B12 deficiency: total B12 less than 180 nanograms (133 pmol) per litre; active B12 less than 25 pmol per litre.

• Indeterminate test result – possible vitamin B12 deficiency: total B12 between 180 and 350 nanograms (133 and 258 pmol) per litre; active B12 between 25 and 70 pmol per litre.

• Vitamin B12 deficiency unlikely: total B12 more than 350 nanograms (258 pmol) per litre; active B12 more than 70 pmol per litre.

FBC and blood film

Identification of hypersegmented neutrophils may suggest either vitamin B12 or folate deficiency; however, they are not sensitive in early vitamin B12 deficiency and are not specific.

Oval macrocytes, hypersegmented neutrophils and circulating megaloblasts in the blood film and megaloblastic change in the bone marrow are the typical features of clinical vitamin B12 deficiency. However, an elevated MCV is not a specific indicator of vitamin B12 deficiency and the possibility of underlying myelodysplastic syndrome has to be considered, as well as excluding alcohol excess, drugs and other causes of an elevated MCV.

The absence of a raised MCV cannot be used to exclude the need for vitamin B12 testing. Associated iron deficiency may result in the MCV being normal, in which case two types of red blood cells may be seen (a dimorphic blood film).

Additional investigations (eg, red cell folate, liver function tests, gamma-glutamyl transpeptidase, thyroid function tests) may be required to rule out other causes of macrocytic anaemia.

Investigations to determine the aetiology of vitamin B12 deficiency⁴

• Consider an anti-intrinsic factor antibody test for people with vitamin B12 deficiency if autoimmune gastritis is suspected and they have not previously had a positive anti-intrinsic factor antibody test at any time or an operation that could affect vitamin B12 absorption (such as total gastrectomy or complete terminal ileal resection).

• If vitamin B12 deficiency is diagnosed in pregnancy or during breastfeeding and autoimmune gastritis is the suspected cause, offer an anti-intrinsic factor antibody test if the criteria above is met and start treatment with intramuscular vitamin B12 replacement.

• When interpreting anti-intrinsic factor antibody test results, a negative test result does not rule out the presence of autoimmune gastritis.

• If autoimmune gastritis is still suspected despite a negative anti-intrinsic factor antibody test, consider further investigations such as:

  • An anti-gastric parietal cell antibody test.

  • A test to measure gastrin levels.

  • A CobaSorb test to measure whether vitamin B12 can be absorbed.

  • Gastroscopy with gastric body biopsy.

Offer serological testing for coeliac disease where the cause of vitamin B12 deficiency is still unknown after further investigations.

Associated diseases¹

People with pernicious anaemia are at increased risk of developing gastric cancer and there is an association with other autoimmune diseases, including primary hypothyroidism, thyrotoxicosis, Hashimoto's thyroiditis, Addison's disease, type 1 diabetes, hypoparathyroidism and vitiligo.

Management of pernicious anaemia¹⁴

Response to treatment of vitamin B12 deficiency can vary and depends on the cause of the vitamin B12 deficiency. Symptoms may start to improve within 2 weeks, but this may take up to 3 months. It can take much longer for symptoms to disappear altogether. Symptoms may get worse initially during treatment.

Malabsorption as the confirmed or suspected cause of vitamin B12 deficiency

• Lifelong intramuscular vitamin B12 replacement if: autoimmune gastritis is the cause, or suspected cause, of vitamin B12 deficiency, or they have had a total gastrectomy, or a complete terminal ileal resection.

• If vitamin B12 deficiency because of malabsorption that is not caused by autoimmune gastritis, or a total gastrectomy or complete terminal ileal resection (eg, malabsorption caused by coeliac disease, partial gastrectomy or some forms of bariatric surgery): vitamin B12 replacement and consider intramuscular instead of oral vitamin B12 replacement (oral dose should be at least 1 mg a day).

Monitoring for gastric cancer in people with suspected or confirmed autoimmune gastritis

People who have autoimmune gastritis are at higher risk of developing gastric neuroendocrine tumours and may also be at higher risk of developing gastric adenocarcinoma. If suspected or confirmed autoimmune gastritis and new, or worsening, upper gastrointestinal symptoms (eg, dyspepsia, nausea or vomiting):

• Consider referral for a gastrointestinal endoscopy and

• Follow the recommendations for Gastric cancer in NICE's guideline on suspected cancer.⁷

Management of other causes of vitamin B12 deficiency

Dietary vitamin B12 deficiency

• Assess dietary intake and consider further investigations to explore other causes of vitamin B12 deficiency if there is any suspicion that the deficiency is not linked to diet.

• Advise that some supplements do not contain enough, or the right type, of vitamin B12 to be effective and advise an oral supplement that contains at least 1 of the following types of vitamin B12: cyanocobalamin, methylcobalamin or adenosylcobalamin.

• Provide dietary advice to improve B12 intake.

• When offering oral vitamin B12 replacement in pregnancy or during breastfeeding, consider a dosage of at least 1 mg a day.

• Consider intramuscular vitamin B12 injections instead of oral replacement if:

  • Any another condition that may deteriorate rapidly and have a major effect on their quality of life (eg, a neurological or haematological condition such as ataxia or anaemia).

  • Any concerns about adherence to oral treatment.

Medicine-induced vitamin B12 deficiency

• Either intramuscular or oral vitamin B12 replacement, based on clinical judgement and the person's preference, while they are taking the medicine causing the side effect.

• If appropriate, review use of the medicine that is causing the side effect to see if it is still needed or can be changed. Review the need for vitamin B12 replacement if the medicine causing the side effect is stopped or changed and the person no longer has symptoms of vitamin B12 deficiency.

Recreational nitrous oxide use as the cause of vitamin B12 deficiency

• Intramuscular or oral vitamin B12 replacement, based on clinical judgement and the person's preference.

• Advise the person to stop using nitrous oxide recreationally. B12 replacement does not prevent neurological or other B12 deficiency problems developing if they continue to use nitrous oxide (as it will inactivate any B12 that is given).

• Review the need for vitamin B12 replacement if the person stops using nitrous oxide recreationally and they no longer have symptoms of vitamin B12 deficiency.

Unknown causes of vitamin B12 deficiency
Offer vitamin B12 replacement, and consider oral instead of intramuscular vitamin B12 replacement and review response to treatment at the person's first follow-up appointment.

Ongoing care and follow up

Offer an initial follow-up appointment to people who are having vitamin B12 replacement at 3 months after they started treatment, or earlier depending on severity of symptoms, or at 1 month after they started treatment if they are pregnant or breastfeeding.

The National Institute for Health and Care Excellence (NICE) guideline provides further detail regarding appropriate steps at follow-up appointments, depending on the response to treatment.

When to refer¹

• Seek urgent advice from a haematologist if the person has neurological symptoms, or is pregnant.

• Refer to a haematologist if the cause of vitamin B12 or folate deficiency is uncertain following investigations, or the suspected cause is haematological malignancy (urgently refer) or other blood disorder.

• Refer to a gastroenterologist if:

  • Malabsorption of vitamin B12 (other than due to pernicious anaemia) is suspected.

  • The person has pernicious anaemia and gastrointestinal symptoms, especially if there is a suspicion of gastric cancer (eg, co-existing iron deficiency). The urgency of referral will depend on the nature of the symptoms.

• Consider referral to a dietician if vitamin B12 deficiency is thought to be due to a poor diet.

Subclinical deficiency⁶

• Low serum vitamin B12 without anaemia or other significant objective parameters may arise from testing for nonspecific symptoms such as tiredness, especially in the elderly population. This may be described as subclinical deficiency.

• This group may contain previously undiagnosed and 'latent' pernicious anaemia, patients with food malabsorption, patients on medications to reduce gastric acid production and patients on metformin.

• Management should be based on clinical judgement, with second-line tests to demonstrate deficiency in the small number of patients in whom a deficiency is strongly suspected.

• In most patients, the serum vitamin B12 assay should be repeated after 1-2 months. The serum level may then return as normal and no further investigation is recommended.

• In those where repeat sampling still falls within the 'subclinical' range, a blood sample should be taken for IFAB and a short trial of empirical therapy (oral cyanocobalamin 50 micrograms daily for four weeks) should be given while awaiting results of IFAB, with instructions to the patient to report immediately if symptoms of neuropathy develop, since this dose would be inadequate for a true pernicious anaemia.

• The short course of vitamin B12 may be of benefit since the elderly have a high incidence of food malabsorption, with some early studies suggesting possible cognitive improvement after vitamin B12 supplements.

• If IFAB is positive, the future management is lifelong therapy.

• If IFAB is negative, a further serum vitamin B12 level is recommended after 3-4 months. If well within the reference range, food malabsorption is a strong possibility and it should be managed accordingly. If still within the 'subclinical' range, consider investigation (plasma methylmalonic acid or holotranscobalamin) to confirm biochemical deficiency.

• In patients with a reduced serum vitamin B12 and normal holotranscobalamin and plasma methylmalonic acid no further action is required since a normal plasma methylmalonic acid and holotranscobalamin indicates an absence of a vitamin B12 deficient state.

• If subclinical deficiency is confirmed then lifelong therapy with vitamin B12 should be considered.

Complications of pernicious anaemia¹

• People with pernicious anaemia are at increased risk of developing gastric cancer (2–3% of all cases of pernicious anaemia), and there is an association with other autoimmune diseases (including myxoedema, thyrotoxicosis, Hashimoto's disease, Addison's disease, and vitiligo).

• Severe anaemia causes a risk of cardiopulmonary complications.

• Neurological changes can occur, even when there are no changes in the blood count. These include paraesthesia, ataxia, peripheral neuropathy (legs usually affected more than the arms), visual disturbance, psychiatric abnormalities and memory loss. Subacute combined degeneration of the spinal cord may also occur.

• Vitamin B12 deficiency predisposes to neural tube defects (such as spina bifida, anencephaly, and encephalocele) in the fetus.

• Deficiency of vitamin B12 or folate may cause ineffective production of any type of blood cells derived from bone marrow.

• Vitamin B12 or folate deficiency may cause sterility. This is reversible with appropriate vitamin supplementation.

Prognosis¹

Before the advent of treatment with B12, the disease was fatal. Hence the name 'pernicious'. However, pernicious anaemia responds rapidly to replacement therapy and most patients have a normal lifespan with little morbidity. If the deficiency has been severe and prolonged, any neurological complications may be irreversible.