Hemolysis - Overview

• Extravascular destruction: damaged RBCs destroyed in liver; spherocytes cleared by spleen (cords of Billroth)
  • Intrinsic defects: G6PD, hemoglobinopathies (e.g. sickle cell, thalessemia), membrane defects (e.g. spherocytosis)
  • Extrinsic damage: antibodies, hypersplenism
• Intravascular destruction: requires significant structural damage to RBC membrane
  • Causes:
    • Trauma
    • Shear stress: valve, microangiopathy
    • Complement-mediated lysis (PNH)
    • Osmotic lysis from hypotonic solutions
    • Toxins (e.g. clostridium)
  • Lysed hemoglobin in plasma binds to haptoglobin, which is cleared by liver
  • Free hemoglobin is also filtered by the kidney

Diagnosis:

• Reticulocytosis: normal bone marrow response to anemia (need to correct for Hct as well as maturation time via reticulocyte index)
• Jaundice with indirect bilirubin, absence of bilirubin in urine (unconjugated bilirubin is not soluble), gallstones
• RBC morphology: spherocytes, schistocytes
• Increased LDH (released from RBCs), decreased haptoglobin - normal LDH and haptoglobin >25 92% sensitive in ruling out hemolysis
• Direct Coombs’ test: RBCs washed, then reacted with antisera to IgG and C3d - if antibodies present, will RBCs will agglutinate

(Christopher Woo MD, 6/9/11)