Rarely, anemia is due to problems that cause the red blood cells (RBCs) to die or be destroyed prematurely. Normally, RBCs live in the blood for about four months. In hemolytic anemia, this time is shortened, sometimes to only a few days. The bone marrow is not able to produce new RBCs quickly enough to replace those that have been destroyed, leading to a decreased number of RBCs in the blood, which in turn leads to a diminished capacity to supply oxygen to tissues throughout the body. This results in the typical symptoms of anemia.
Depending on the cause, hemolytic anemia can be chronic, developing and lasting over a long period or lifetime, or may be acute. The various forms can have a wide range of signs and symptoms. See the discussions of the various types below for more on this.
The different causes of hemolytic anemia fall into two main categories:
- Inherited forms in which a gene or genes are passed from one generation to the next that result in abnormal RBCs or hemoglobin
- Acquired forms in which some factor results in the early destruction of RBCs
Inherited Hemolytic Anemia
Two of the most common causes of inherited hemolytic anemia are sickle cell anemia and thalassemia:
Sickle cell anemia is a disorder where the body makes abnormal hemoglobin, which in turn causes red blood cells to become crescent-shaped, sickle cells under certain conditions. The "trait" (when you carry one mutated gene from one of your parents) can cause minor difficulties; the "disease" (when you carry two mutated genes, one from each of your parents) causes severe clinical problems. Misshapen blood cells are unstable (leading to hemolysis) and can block blood vessels, causing pain and anemia. Newborns are usually screened for sickle cell anemia, particularly those of African descent, because they are more likely to possess the inherited trait. Sometimes screening is done prenatally on a sample of amniotic fluid. Follow-up tests for hemoglobin variants may be performed to confirm a diagnosis. Treatment is usually based on the type, frequency, and severity of symptoms.
Thalassemia is an inherited blood disorder where there is an imbalance in hemoglobin globin chain production that results in anemia and smaller red blood cells. Only in its most severe form do the RBCs break apart (hemolysis) and have a shortened life span. This "beta major" form (also called Cooley's anemia) may result in growth problems, jaundice, and severe anemia. In milder forms, there is no significant hemolysis. This "beta minor" form (sometimes called beta thal trait) causes a mild anemia and no obvious symptoms.
Other less common types of inherited forms of hemolytic anemia include:
- Hereditary spherocytosis—results in abnormally shaped RBCs (so called spherocytes) that may be seen on a blood smear. These cells are very rigid, cannot pass through the spleen as normal red cells would, and thus get destroyed prematurely.
- Hereditary elliptocytosis—another cause of abnormally oval-shaped RBCs seen on a blood smear.
- Glucose-6-phospate dehydrogenase (G6PD) deficiency—G6PD is an enzyme that is necessary for RBC survival and, if deficient, RBCs come into contact with certain substances in the blood, the cells rupture and get destroyed. Those substances could include naphthalene, antimalarial medications, or fava beans. G6PD deficiency may be diagnosed with a test for its activity.
- Pyruvate kinase deficiency—pyruvate kinase is another enzyme important for RBC survival and its deficiency causes significant anemia. It is a rare disease that may be diagnosed with a test for the enzyme activity.
Since some of these inherited forms may have mild symptoms, they may first be detected on a routine complete blood count (CBC) and blood smear, which can reveal various abnormal results that give clues as to the cause. Follow-up tests are then usually performed to make a diagnosis. Some of these include:
- Hemoglobinopathy evaluation
- DNA analysis—not routinely done but can be used to help diagnose hemoglobin variants, thalassemia, and to determine carrier status
- G6PD test—to detect deficiency in this enzyme
- Osmotic fragility test—detects RBCs that are more fragile than normal, which may be found in hereditary spherocytosis
These genetic disorders cannot be cured, but often the symptoms resulting from the anemia may be alleviated with treatment as necessary.
Acquired Hemolytic Anemia
Some of the conditions or factors involved in acquired forms of hemolytic anemia include:
- Autoimmune disorders—conditions in which the body produces antibodies against its own red blood cells; it is not well understood why this may happen, but it accounts for about half of all cases of hemolytic anemia. Certain diseases such as lupus, HIV and hepatitis can increase a person's risk for it.
- Transfusion reaction—result of blood donor-recipient incompatibility; this occurs very rarely, but when it does, it can have some serious complications. For more on this, see the article on Transfusion Medicine.
- Infections, such as malaria and infectious mononucleosis (mono)
- Mother-baby blood group incompatibility—may result in hemolytic disease of the newborn
- Medications—certain medications such as penicillin can trigger the body to produce antibodies directed against RBCs or cause the direct destruction of RBCs.
- Physical destruction of RBCs by, for example, an artificial heart valve or cardiac bypass machine used during open-heart surgery
- Paroxysmal Nocturnal Hemoglobinuria (PNH)—a rare condition in which the different types of blood cells including RBCs, white blood cells, and platelets are abnormal due to lack of certain surface proteins; because the RBCs are defective, the body destroys them earlier than the normal lifespan. This disease occurs due to a change or mutation in a gene called PIGA in the stem cells that make blood. Though it is a genetic disorder, it is not passed from one generation to the next (it is not an inherited condition). Those affected will often pass dark urine due to the hemoglobin released by destroyed RBCs being cleared from the body by the kidneys. This is most noticeable first thing in the morning when urine is most concentrated. For more on this, see this Genetic Home Reference webpage.
Hemolytic anemias are often first identified by signs and symptoms, during physical examination, and by medical history. A medical history can reveal, for example, a recent transfusion, treatment with penicillin, or cardiac surgery. A CBC and/or blood smear may show various abnormal results. Depending on those findings, additional follow-up tests may be performed. Some of these may include:
- Tests for autoantibodies for suspected autoimmune disorders
- Direct antiglobulin test (DAT) in the case of transfusion reaction, mother-baby blood type incompatibility, or autoimmune hemolytic anemia
- Haptoglobin—usually low
- Reticulocyte count—typically high
- Flow cytometry for suspected PNH
Treatments for hemolytic anemia are as varied as the causes. However, the goals are the same: to treat the underlying cause of the anemia, to decrease or stop the destruction of RBCs, and to increase the RBC count and/or hemoglobin level to alleviate symptoms. This may involve, for example:
- Drugs used to suppress production of autoantibodies that destroy RBCs
- Blood transfusions to increase the number of healthy RBCs
- Bone marrow transplant—to increase production of normal RBCs
- Avoiding triggers that cause the anemia such as the cold in some forms of autoimmune hemolytic anemia or fava beans, naphthalene and certain medicines for those with G6PD deficiency.