What is the Difference Between Intravascular and Extravascular Hemolysis?

Intravascular and extravascular hemolysis are two different mechanisms of red blood cell (RBC) destruction that contribute to hemolytic anemia. The main differences between them are:

1. Location: Intravascular hemolysis occurs primarily within blood vessels, where RBCs are destroyed in the blood vessel itself. In contrast, extravascular hemolysis takes place within macrophages in the liver and spleen.
2. Hemoglobin release: Intravascular hemolysis results in the release of free hemoglobin into the plasma, which can lead to hemoglobinemia and hemoglobinuria (positive blood on urine tests). In contrast, extravascular hemolysis does not release free hemoglobin into the plasma, so it does not cause hemoglobinemia or hemoglobinuria unless it is accompanied by intravascular hemolysis.
3. Causes: Examples of intravascular hemolysis include enzyme defects such as glucose-6-phosphate dehydrogenase deficiency. Extravascular hemolysis is more common in cases of RBC membrane disorders such as hereditary spherocytosis and autoimmune hemolytic anemia.

Clinical presentation of hemolytic anemia can vary greatly, ranging from mild anemia with asymptomatic splenomegaly, to jaundice with splenomegaly and dark urine, to acute severe anemia. While extravascular hemolysis is always occurring, it is most often seen alone without intravascular hemolysis. However, some patients with specific causes of hemolytic anemia may experience concurrent intravascular and extravascular hemolysis.

Comparative Table: Intravascular vs Extravascular Hemolysis

Intravascular and extravascular hemolysis are two mechanisms by which hemolysis takes place. Here is a table highlighting their differences:

Some forms of hemolytic anemia feature both intravascular and extravascular hemolysis, and the degree of anemia depends on how rapidly the red blood cells are being removed from circulation.