Hemolytic anemia is a condition in which there are not enough red blood cells in the blood, due to the premature destruction of red blood cells. There are a number of specific types of hemolytic anemia, which are described individually.

Hemolytic anemia occurs when the bone marrow is unable to increase production to make up for the premature destruction of red blood cells. If the bone marrow is able to keep up with the early destruction, anemia does not occur (this is sometimes called compensated hemolysis).

There are many types of hemolytic anemia, which are classified by the reason for the premature destruction of red blood cells. The defect may be in the red blood cell itself (intrinsic factors), or outside the red blood cell (extrinsic factors).

Intrinsic factors are often present at birth (hereditary). They include:

• Abnormalities in the proteins that build normal red blood cells
• Differences in the protein inside a red blood cell that carries oxygen (hemoglobin)

Extrinsic factors include:

• Abnormal immune system responses
• Blood clots in small blood vessels
• Certain infections
• Side effects from medications

Types of hemolytic anemia include:

• Hemoglobin SC disease (similar in symptoms to sickle-cell anemia)
• Hemolytic anemia due to G6PD deficiency
• Hereditary elliptocytosis
• Hereditary ovalocytosis
• Hereditary spherocytosis
• Idiopathic autoimmune hemolytic anemia
• Malaria
• Microangiopathic hemolytic anemia (MAHA)
• Non-immune hemolytic anemia caused by chemicals or toxins
• Paroxysmal nocturnal hemoglobinuria (PNH)
• Secondary immune hemolytic anemia
• Sickle-cell anemia
• Thalassemia
• Transfusion of blood from a donor with a different blood type