hemolysis

hemolysis, breakdown or destruction of red blood cells so that the contained oxygen-carrying pigment hemoglobin is freed into the surrounding medium.

Hemolysis occurs normally in a small percentage of red blood cells as a means of removing aged cells from the bloodstream and freeing heme for iron recycling. It also can be induced by exercise.

In disease, hemolysis typically is associated with hemolytic anemia, whereby increased or accelerated hemolysis shortens the life span of red blood cells, causing them to die more quickly than they can be replenished by the bone marrow. Hemolytic anemia may involve either intravascular hemolysis, in which red blood cells are destroyed within the circulation, or extravascular hemolysis, in which the cells are destroyed in the liver or spleen. The cause may be intrinsic or extrinsic in nature. Causes of intrinsic hemolytic anemia include inherited defects in red blood cells, such as hereditary spherocytosis, sickle cell anemia, and thalassemia. Extrinsic disease may be caused by antibodies that attack and destroy red blood cells, such as in paroxysmal cold hemoglobinuria (a type of autoimmune hemolytic anemia); by diseases or infections that cause the spleen to become overactive (hypersplenism); or by other factors that result in the destruction of red blood cells, including chemicals, infections, trauma (such as repeated impact of the feet in running), venoms, or the toxic products of microorganisms. In erythroblastosis fetalis (hemolytic disease of the newborn), a mismatch in antibody compatibility between fetal and maternal blood results in the destruction of fetal red blood cells by maternal antibodies that cross the placenta.

Hemolysis may be produced in the laboratory by various physical agents: heat, freezing, flooding with water, sound. In certain situations it is used as a specific laboratory test for antigen–antibody reactions.