Red Cell Staining (Color)

Central pallor

• Introduction
  • A normal red blood cell has a biconcave disk shape. Because the center is much thinner than the periphery, it creates the illusion of a Hb-free center on a peripheral smear. The area of pallor in its center (about 1/3 of the diameter of the cell) when viewed under the light microscope. 

• • • The area of central pallor may be:
      • Normal (normochromia)
      • Increased (hypochromia)
      • Decreased (hyperchromia)
    • The color can be evaluated by the mean corpuscular hemoglobin concentration (MCHC). 
• Hypochromia
  • Hypochromic red blood cells have less color (> 1/3 central pallor) than normal when examined under a microscope. 
  • The decrease in redness is due to a disproportionate reduction of red cell hemoglobin (the pigment that imparts the red color) in proportion to the volume of the cell. 
  • Hypochromia correlates with a lower than normal MCHC. 
  • The MCHC, in turn, is helpful in distinguishing between causes of microcytic anemia. 
  • Differential diagnosis of hypochromia includes:
    • Iron deficiency 
    • Thalassemia intermedia/major
    • Anemia of inflammation
    • Sideroblastic anemia
• Hyperchromia
  • Refers to an increase in the intensity of red blood cell color.
  • The area of central pallor is decreased or gone.
  • Correlates with a higher than normal MCHC. 
  • Hyperchromic cells may be:
    • Spherocytes
    • Microspherocytes
    • Sickle cells
    • Spur cells
    • Schistocytes
    • HbC cells
  • Differential diagnosis includes:
    • Spurious
    • Autoimmune hemolytic anemia
    • Hereditary spherocytosis
    • HbC
    • Spur cell anemia
    • Microangiopathic hemolytic anemia

Polychromatophilia

• Immature non-nucleated red cells with a blue hue in their cytoplasm.
• The blue may be barely visible or may be marked.
• Polychromatic red cells are typically larger than normal red cells.
• They tend to lack central pallor.
• When stained with supravital dyes the remaining mRNA and ribosomes give the red cells a “reticular” mesh-like network, hence the name “reticulocyte”.
• Of note, white the vast majority of polychromatophilic cells are reticulocytes (as defined by the presence of reticulum on a reticulocyte stain), not all reticulocytes are recognized as polychromatophils on the Wright-Giemsa stain.

Peripheral smear from a 25-year-old woman with GI bleed shows multiple polychromatophilic red cells (polychromatophilia) 100x (oil).