Anaemia, Megaloblastic

Description

General measures

Medicine treatment

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D51.0-2/D51.2/D51.8-9/D52.0-1/D52.8-9/D53.1/D53.8-9

DESCRIPTION

• Anaemia caused by a deficiency of folate and/or vitamin B₁₂.
• Note that several medicines can cause macrocytic anaemia (e.g. hydroxyurea, methotrexate, zidovudine, azathioprine, valproic acid, and phenytoin) without deficiencies of folate and/or vitamin B₁₂.
• Clinical manifestations of vitamin B₁₂ deficiency are mainly neurological – peripheral neuropathy, dementia and subacute combined degeneration of the spinal cord.

Investigations

• Elevated MCV (>100 fl) and MCH (>34 pg).
• Pancytopaenia in severe cases.
• FBC and peripheral smear: oval macrocytes, hypersegmentation of neutrophils, thrombocytopenia with giant platelets.
• Decreased serum vitamin B₁₂ and/or red blood cell folate.
• Intrinsic factor antibodies, and/ or anti-parietal cell antibodies are found in pernicious anaemia.

GENERAL MEASURES

• Counsel on dietary modifications to ensure adequate intake of folate and vitamin B₁₂ (especially important in vegetarians and malnourished patients).
• Identify and treat the underlying cause, e.g. antibiotics for bacterial intestinal overgrowth.
• Chronic metformin use can lead to vitamin B₁₂ deficiency by interfering with absorption. Maintain a low threshold for clinical features of vitamin B₁₂ deficiency in patients on metformin, and check serum levels if clinically indicated.

MEDICINE TREATMENT

• Start with folic acid and vitamin B₁₂ supplementation after taking blood samples for RBC folate and serum vitamin B₁₂ levels.
• Monitor serum potassium and replace if necessary.
• Adjust management according to results.

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CAUTION
Give vitamin B₁₂ and folic acid together until the test results are available, as giving folic acid alone in patients with a vitamin B₁₂ deficiency may precipitate a permanent neurological deficit.

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Folic acid deficiency

• Folic acid, oral, 5 mg daily until Hb returns to normal (see reference ranges in Anaemia).

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Note:
Prolonged treatment may be required for malabsorption states.

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Vitamin B₁₂ deficiency

For uncomplicated pernicious anemia:

• Vitamin B₁₂, IM, 1 mg on alternate days for 1–2 weeks.
  • Followed by 1 mg weekly until blood count is normal.
  • Lifelong maintenance dose: 1 mg monthly.

For serious complications from deficiency:

• Vitamin B₁₂ IM, 1 mg daily for 1 week.
  • Followed by 1 mg weekly for 1 month.
  • Lifelong maintenance dose: 1 mg monthly.

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Consider the following in the event of response failure:

• Co-existing folate and/or iron deficiency,
• Other causes of macrocytosis:
  - Myelodysplasia,
  - Hypothyroidism,
  - Chronic alcohol use,
• Drug-induced, e.g. hydroxyurea, methotrexate, zidovudine, azathioprine, valproic acid and phenytoin.

Prophylaxis:

O99.0/Z49.1/Z29.2

Vitamin B₁₂ prophylaxis:

Vitamin B₁₂ is indicated for patients after total gastrectomy or ileal resection:

• Vitamin B₁₂, IM, 1 mg every second month for life.

Folic acid prophylaxis:

Indications:

• Chronic inherited or acquired haemolytic anaemias, e.g. sickle cell anaemia, thalassaemia
• Myeloproliferative disorders
• Exfoliative skin disorders
• Increased demands, e.g. pregnancy, chronic haemodialysis
• Folic acid, oral, 5 mg daily.

Click here for the pdf.

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Standard Treatment Guidelines And Essential Medicines List For South Africa, Adult Hospital level_Version 1_30 March 2026

Chapter 2: Blood and Blood Forming Organs; 2.1.2 Anaemia, Megaloblastic