That is, instead of being collected at the end of its useful life and disposed of normally, the RBC disintegrates in a manner allowing free iron-containing molecules to reach the blood. With their complete lack of mitochondria, RBCs rely on pentose phosphate pathway (PPP) for the materials needed to reduce oxidative damage. Any limitations of PPP can result in more susceptibility to oxidative damage and a short or abnormal lifecycle. If the cell is unable to signal to the reticuloendothelial phagocytes by externalizing phosphatidylserine, it is likely to lyse through uncontrolled means.The distinguishing feature of intravascular hemolysis is the release of RBC contents into the blood stream. The metabolism and elimination of these products, largely iron-containing compounds capable of doing damage through Fenton reactions,  is an important part of the condition. Several reference texts exist on the elimination pathways, for example. Free hemoglobin can bind to haptoglobin, and the complex is cleared from the circulation; thus, a decrease in haptoglobin can support a diagnosis of hemolytic anemia. Alternatively, hemoglobin may oxidize and release the heme group that is able to bind to either albumin or hemopexin. The heme is ultimately converted to bilirubin and removed in stool and urine. Hemoglobin may be cleared directly by the kidneys resulting in fast clearance of free hemoglobin but causing the continued loss of hemosiderin loaded renal tubular cells for many days. Additional effects of free hemoglobin seem to be due to specific reactions with NO.
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.