Megaloblastic anemia is anemia resulting from a deficiency of vitamin B12 and folic acid.

Causes

• nutritional defects (vitamin B12 is mainly from animal sources, and vegans may require supplementation)
• chronic liver diseases
• decreased production of intrinsic factor (this disease entity is called pernicous anemia)
• intestinal malabsorption (due to an enteritis, celiac disease or other causes).
• fish tab worm infestation (Diphylobothrium latum)

Hematological findings

The blood film can point towards vitamin deficiency:

• Decreased red blood cell (RBC) count and hemoglobin levels
• Increased mean corpuscular volume (MCV, >100 fl) and mean corpuscular hemoglobin (MCH)
• The reticulocyte count is normal
• The platelet count may reduced.
• Neutrophil granulocytes may show multisegmented nuclei ("senile neutophil"). This is thought to be due to decreased production and a compensatory prolonged lifespan for circulating neutrophils.
• Anisocytosis (increased variation in RBC size) and poikilocytosis (increased numbers of abnormally shaped RBCs).
• Bone marrow (not normally checked in a patient suspected of megaloblastic anemia) shows megaloblastic hyperplasia.

Analysis

The Schilling test is often performed to determine the nature of the vitamin B12 deficiency.