Hemolytic anemia is a blood condition that occurs when your red blood cells are destroyed faster than they can be replaced. Hemolytic anemia can develop quickly or slowly, and it can be mild or serious. What causes hemolytic anemia? Hemolytic anemia may be caused by inherited conditions that affect the red blood cells. It's also caused by certain infections or if someone receives a blood transfusion from a donor whose blood type didn't match.