Macrocytic anemia causes

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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]

Causes

Normal B12 absorption and action are dependent of 5 things: dietary intake, acid in the stomach, pancreatic secretions, secretion of IF by Gastric parietal cells, an ileum that can absorb the IF-B12 complex

• Vitamin B12 Deficiency:

1. Deficient intake
2. Deficient intrinsic factor (pernicious anaemia or gastrectomy)
3. Bilogical competition for B12 by diverticulosis, fistula, intestinal anastomosis, achlorhydria and infection by the marine parasite Diphyllobothrium latum
4. Selective B12 malabsorption (congenital and drug-induced)
5. Chronic pancreatitis
6. Ileal resection and bypass

• Folate Deficiency:

1. Deficient intake.
2. Increased needs: pregnancy, infant, rapid cellular proliferation, and cirrhosis
3. Malabsorption (congenital and drug-induced)
4. Intestinal and jejunal resection

• Combined Dieficiency (Tropical Sprue): Vitamin B12 & Folate.
• Inherited DNA Synthesis Disorders: Deficient thiamine and factors (e.g. enzymes) responsible for folate metabolism.
• Toxins and Drugs:
  • Cytarabine
  • Folic acid antagonists (methotrexate)
  • Purine antagonists (6-mercaptopurine)
  • Pyrimidine antagonists (cytosine arabinoside)
  • Phenobarbital
  • Erythroleukemia.

• In general:

• Nutritional defects (folic acid or vitamin B12 which is mainly from animal sources; vegans may require supplementation)
• Chronic liver diseases
• Alcoholism
• Pregnancy
• Decreased production of intrinsic factor (this disease entity is called pernicious anemia)
• Intestinal malabsorption (due to an enteritis, celiac disease or other causes).
• Fish tapeworm infestation (Diphyllobothrium latum)
• Failure to replicate chromosomes due to lack of thymidine.
• Lesch-Nyhan Syndrome
• Cytotoxic drugs interfering with DNA synthesis
• intestinal flora disruption due to antibiotic use