Hemolytic anemia

Hemolytic anemia

Updated: 07/26/2024

© Jun Wang, MD, PhD

 

General features

  • Caused by increase in red cell destruction
  • Extravascular or intravascular hemolysis
  • No detectable anemia until the average RBC lifespan < 30 days

Extravascular hemolysis

  • RBCs removed by RE system and broken down
  • Characterized by 

o   Anemia

o   Splenomegaly

o   Jaundice

  • Destruction of RBCs usually by phagocytes

Intravascular hemolysis

  • RBCs ruptured within the blood vessel
  • Three pathways

o   Complement fixation and direct lysis (most commonly IgM-mediated)

o   Mechanical, shear-force associated, as seen in microangiopathic hemolysis in hemolytic-uremic syndrome, and thrombotic thrombocytopenic purpura

o   Membrane or Hb abnormality associated, such as HbS, hereditary spherocytosis

  • Common causes

o   Mismatched blood transfusion (usually ABO)

o   G6PD deficiency with oxidant stress

o   Drug, infection or autoimmune Paroxysmal nocturnal hemoglobinuria

o   Unstable hemoglobin

Clinical features

  • Acute or chronic clinical courses
  • Symptoms of anemia
  • Pallor of mucous membranes
  • Jaundice: Elevated uncongugated bilirubin
  • Splenomegaly (with extravascular hemolysis)
  • Dark urine due to increased urobilinogen or hemoglobinuria
    • While urobilinogen is colorless, it can be oxidized to yellow urobilin 
    • Hemoglobinuria tend to be pink to brown, depending on the level of Hb
  • Pigment gallstones
  • Thrombotic complications

o   Hypercoagulable state associated with chronic hemolysis

o   Thrombosis subsequent to splenectomy

Common causes

o   Sickle cell anemia

o   HbC, HbE disease

  • Metabolic defect

o   G6PD deficiency

o   Pyruvate kinase deficiency

  • Structural defect

o   Hereditaryspherocytosis

o   Paroxysmalnocturnal hemoglobinuria

Laboratory findings

  • Features of increased RBC breakdown

o   High serum LDH, bilirubin, urine urobilinogen, hemoglobinuria

o   Low serum haptoglobin (chelation of free Hb, more common in intravascular hemolysis

  • Features of increased RBC production

o   Reticulocytosis

o   Bone marrow erythroid hyperplasia

  • RBC abnormalities

o   Morphology: schistocytes or spherocytes

  • Other tests

o   Specific enzymes, proteins or DNA test, anti-RBC Igs

 

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