Anaemia, megaloblastic

D53.1/D58.9/D59.9/D55.0-3/D55.8-9/D56.0-4/D56.8-9/D57.0-3/D57.8/D58.0-2/ D58.89/D47.1/L26

DESCRIPTION

Anaemia caused by a deficiency of folate and/or vitamin B12.
Note that several medicines can cause macrocytic anaemia (e.g. hydroxyurea, stavudine and zidovudine) without deficiencies of folate and/or vitamin B12.

Investigations

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

GENERAL MEASURES

Dietary modifications to ensure adequate intake of folate and vitamin B12 (important in vegetarians and malnourished patients).
Identify and treat the underlying cause, e.g. antibiotics for intestinal overgrowth with bacteria.

Metformin use can lead to vitamin B12 deficiency by interfering with absorption.

MEDICINE TREATMENT

After blood samples for RBC folate and vitamin B12 levels have been taken, start with folic acid and vitamin B12 supplementation.
Monitor serum potassium and replace if necessary.
Adjust management according to results.

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

Folic acid deficiency

  • Folic acid, oral, 5 mg daily until Hb returns to normal.

Prolonged treatment may be required for malabsorption states.

Vitamin B12 deficiency

  • Vitamin B12 , IM.
    • 1 mg daily for 5 days, then weekly for a further 3 doses
    • Follow with 1 mg every second month for life in patients with pernicious anaemia.

NOTE:

  • Response to treatment is associated with an increase in energy and strength and improved sense of well-being.
  • Reticulocytosis begins 3–5 days after therapy and peaks at about day 7.
  • Anaemia normally corrects within 1–2 months. The white cell count and platelets normalise in 7–10 days. As there is an increase in red blood cell production, iron and folic acid supplementation is also recommended, until Hb has normalised. Check for hypokalaemia in the first few days of therapy.

Hypokalaemia: See Hypokalaemia.

Consider the following if there is failure to respond:

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

Prophylaxis O99.0/Z49.1/Z29.2

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

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

Indications for folic acid:

  • 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.