In this case little hemoglobin escapes into blood plasma. The macrophages of the reticuloendothelial system in these organs engulf and destroy structurally-defective red blood cells, or those with antibodies attached, and release unconjugated bilirubin into the blood plasma circulation. Typically, the spleen destroys mildly abnormal red blood cells or those coated with IgG-type antibodies, while severely abnormal red blood cells or those coated with IgM-type antibodies are destroyed in the circulation or in the liver.If extravascular hemolysis is extensive, hemosiderin can be deposited in the spleen, bone marrow, kidney, liver, and other organs, resulting in hemosiderosis.In a healthy person, a red blood cell survives 90 to 120 days in the circulation, so about 1% of human red blood cells break down each day. The spleen (part of the reticulo-endothelial system) is the main organ that removes old and damaged RBCs from the circulation. In healthy individuals, the breakdown and removal of RBCs from the circulation is matched by the production of new RBCs in the bone marrow.In conditions where the rate of RBC breakdown is increased, the body initially compensates by producing more RBCs; however, breakdown of RBCs can exceed the rate that the body can make RBCs, and so anemia can develop. Bilirubin, a breakdown product of hemoglobin, can accumulate in the blood, causing jaundice.In general, hemolytic anemia occurs as a modification of the RBC life cycle.
Immune-mediated causes could include transient factors as in Mycoplasma pneumoniae infection (cold agglutinin disease) or permanent factors as in autoimmune diseases like autoimmune hemolytic anemia (itself more common in diseases such as systemic lupus erythematosus, rheumatoid arthritis, Hodgkins lymphoma, and chronic lymphocytic leukemia). Spur cell hemolytic anemia
Any of the causes of hypersplenism (increased activity of the spleen), such as portal hypertension. Acquired hemolytic anemia is also encountered in burns and as a result of certain infections (e.g. malaria). Paroxysmal nocturnal hemoglobinuria (PNH), sometimes referred to as Marchiafava-Micheli syndrome, is a rare, acquired, potentially life-threatening disease of the blood characterized by complement-induced intravascular hemolytic anemia. Lead poisoning resulting from the environment causes non-immune hemolytic anemia. Similarly, poisoning by arsine or stibine also causes hemolytic anemia. Runners can develop hemolytic anemia due to "footstrike hemolysis", owing to the destruction of red blood cells in feet at foot impact. Low-grade hemolytic anemia occurs in 70% of prosthetic heart valve recipients, and severe hemolytic anemia occurs in 3%. Mechanism
In hemolytic anemia, there are two principal mechanisms of hemolysis; intravascular and extravascular. Intravascular hemolysis
Intravascular hemolysis describes hemolysis that happens mainly inside the vasculature. As a result, the contents of the red blood cell are released into the general circulation, leading to hemoglobinemia and increasing the risk of ensuing hyperbilirubinemia.Intravascular hemolysis may occur when red blood cells are targeted by autoantibodies, leading to complement fixation, or by damage by parasites such as Babesia. Extravascular hemolysis
Extravascular hemolysis refers to hemolysis taking place in the liver, spleen, bone marrow, and lymph nodes.