ANAEMIA, MEGALOBLASTIC
DESCRIPTION
Anaemia caused by a deficiency of folate and/or vitamin B12.
Investigations
Elevated MCV (mean corpuscular volume) and MCH (mean corpuscular
haemoglobin).
Macro-ovalocytes on blood smear; polysegmentation of neutrophils,
thrombocytopenia with giant platelets.
Decreased serum vitamin B12 or red blood cell folate.
Pancytopenia in severe cases.
Intrinsic factor antibodies in vitamin B12 deficiency, and anti-parietal cell
antibodies in pernicious anaemia.
GENERAL MEASURES
Dietary modifications to ensure adequate intake of folate and vitamin B12.
Identify and treat the underlying cause, e.g. antibiotics for intestinal
overgrowth with bacteria.
MEDICINE TREATMENT
After blood samples for RBC, folate and vitamin B12 levels have been taken,
start with folic acid and vitamin B12.
Monitor serum potassium and replace if necessary.
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.
Adjust management according to results.
Folic acid deficiency
Folic acid, oral, 5 mg daily until haemoglobin returns to normal.
Prolonged treatment may be required for malabsorption states.
Vitamin B12 deficiency
Vitamin B12, IM.
o 1 mg daily for 5 days, then weekly for a further 3 doses
o Follow with 1 mg every second month for life in patients with
pernicious anaemia, except in patients with clearly modifiable
nutritional deficiency.
Note:
Response to treatment is associated with an increase in strength and
improved sense of well-being.
Reticulocytosis begins 3–5 days after therapy and peaks at about day 7.
The anaemia is corrected 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, short-term iron and folic acid supplementation is also
recommended.
Consider the following if there is failure to respond:
» co-existing folate and/or iron deficiency,
» infection,
» hypothyroidism,
» myelodysplasia,
» incorrect diagnosis,and
» drug-induced, e.g. hydroxyurea, stavudine and zidovudine.
Prophylaxis
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 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.
Reference and further reading
Standard Treatment Guidelines and Essential Medicines List for South Africa 2012 Edition
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