Causes of non-megaloblastic macrocytosis

• Alcohol (may not be associated with anaemia)
• Liver disease (may not be associated with anaemia)
• Hypothyroidism (may not be associated with anaemia)
• Marrow failure (associated with anaemia)
  • Myelodysplasia, myeloma, anaplastic anaemia

Spurious (false) macrocytosis

• The volume of the mature red cell is normal, but the MCV is measured as high
• Important examples include:
  • Reticulocytosis in response to acute blood loss or red cell breakdown - reticulocytes are bigger than mature red cells
  • Cold-agglutinins - cause RBCs to clump at temperatures lower than core body temperature, making them appear as one giant cell
    • Ensure sample is warmed to 37℃