Hemolytic Anemia 

Hemolysis is the premature destruction of erythrocytes. A hemolytic anemia will develop if bone marrow activity cannot compensate for the erythrocyte loss. The severity of the anemia depends on whether the onset of hemolysis is gradual or abrupt and on the extent of erythrocyte destruction. Mild hemolysis can be asymptomatic while the anemia in severe hemolysis can be life threatening and cause angina and cardiopulmonary decompensation.

The clinical presentation also reflects the underlying cause for hemolysis. For example, sickle cell anemia (see the image below) is associated with painful occlusive crises. (See Clinical.)

There are multiple causes for hemolytic anemia, and the clinical presentation can differ depending on the etiology. An array of laboratory tests are available for detecting hemolysis, and specialized tests may be indicated to diagnose the cause for hemolysis (see Workup). There are differences in the management of various types of hemolytic anemias (see Treatment).

Go to Anemia, Iron Deficiency Anemia, and Chronic Anemia for complete information on these topics.

Hemolysis can be due to hereditary and acquired disorders. The etiology of premature erythrocyte destruction is diverse and can be due to conditions such as intrinsic membrane defects, abnormal hemoglobins, erythrocyte enzymatic defects, immune destruction of erythrocytes, mechanical injury, and hypersplenism.

Hemolysis may be an extravascular or an intravascular phenomenon. Autoimmune hemolytic anemia and hereditary spherocytosis are examples of extravascular hemolysis because the red blood cells are destroyed in the spleen and other reticuloendothelial tissues.^[1] Intravascular hemolysis occurs in hemolytic anemia due to prosthetic cardiac valves, G-6-PD deficiency, thrombotic thrombocytopenic purpura, disseminated intravascular coagulation, following transfusion of ABO incompatible blood, and paroxysmal nocturnal hemoglobinuria (PNH). Hemolysis may also be intramedullary when fragile RBC precursors are destroyed in the bone marrow prior to release into the circulation. Intramedullary hemolysis occurs in pernicious anemia and thalassemia major.

Hemolysis is associated with a release of RBC lactate dehydrogenase (LDH). Hemoglobin released from damaged RBC leads to an increase in indirect bilirubin and urobilinogen.

A patient with mild hemolysis may have normal hemoglobin levels if increased RBC production matches the rate of RBC destruction. However, patients with mild hemolysis may develop marked anemia if their bone marrow erythrocyte production is transiently shut off by viral (parvovirus B-19) or other infections. This scenario would be an aplastic crisis since the bone marrow can no longer compensate for ongoing hemolysis.

Skull and skeletal deformities can occur in childhood due to a marked increase in hematopoiesis and resultant bone marrow expansion in disorders such as thalassemia.

The various types of hemolytic anemia have been documented.^{[2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14]} Only the more commonly encountered hemolytic disorders are discussed in this article.

Hereditary disorders include erythrocyte membrane, enzymatic defects, and hemoglobin abnormalities. Hereditary disorders include the following:

• Glucose-6-phosphate dehydrogenase (G-6-PD) deficiency
• Hereditary spherocytosis
• Sickle cell anemia

Acquired causes of hemolysis include immune disorders, toxic chemicals and drugs,^{[3, 8, 15]} antiviral agents (eg, ribavirin^[16] ) physical damage, and infections.^[17]

Autoimmune hemolytic anemia (AIHA) can be due to warm or cold autoantibody types; and rarely, mixed types.^{[18, 19, 20]} Most warm autoantibodies belong to the immunoglobulin IgG class. These antibodies can be detected by a direct Coombs test, which also is known as a direct antiglobulin test (DAT). AIHA may occur after allogeneic hematopoietic stem cell transplantation. The 3-year cumulative incidence in this population has been reported at 4.44%.^[21]

Microangiopathic hemolytic anemia is found in patients with defective prosthetic cardiac valves, disseminated intravascular coagulation (DIC), hemolytic uremic syndrome (HUS), and thrombotic thrombocytopenic purpura (TTP).^{[22, 23]} Fragmented erythrocytes (schistocytes) are seen in microangiopathic hemolytic anemias.^[4]

In PNH, hemolysis is due to intravascular complement-mediated destruction of erythrocytes.

Hemolytic anemia represents approximately 5% of all anemias. Acute AIHA is relatively rare, with an incidence of 1-3 cases per 100,000 population per year.^[24]

Hemolytic anemias are not specific to any race. However, sickle cell disorders are found primarily in Africans, African Americans, some Arabic peoples, and Aborigines in southern India.

Several variants of G-6-PD deficiency exist. The A(-) variant is found in West Africans and African Americans. Approximately 10% of African Americans carry at least 1 copy of the gene for this variant. The Mediterranean variant occurs in individuals of Mediterranean descent and in some Asians.

Most cases of hemolytic anemia are not sex specific. However, AIHA is slightly more likely to occur in females than in males. G-6-PD deficiency is an X-linked recessive disorder. Therefore, males are usually affected, and females are carriers.

Although hemolytic anemia can occur in persons of any age, hereditary disorders are usually evident early in life. AIHA is more likely to occur in middle-aged and older individuals.

The prognosis for patients with hemolytic anemia depends on the underlying cause.

Overall, mortality rates are low in hemolytic anemias. However, the risk is greater in older patients and patients with cardiovascular impairment.

Morbidity depends on the etiology of the hemolysis and the underlying disorder such as sickle cell anemia or malaria.

Patients should be able to identify symptoms and signs of the recurrence of hemolysis. They should seek prompt medical attention if symptoms reoccur.

Patients with G-6-PD deficiency should know which medications to avoid.

For patient education information, see the Blood and Lymphatic System Center, as well as Anemia.