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Hemolytic anemia is a form of
anemia due to
hemolysis, the abnormal breakdown of
red blood cells (RBCs), either in the
blood vessels (intravascular hemolysis) or elsewhere in the human body (extravascular). It has numerous possible causes, ranging from relatively harmless to life-threatening. The general classification of hemolytic anemia is either
inherited or acquired. Treatment depends on the cause and nature of the breakdown.
Symptoms of hemolytic anemia are similar to other forms of anemia (
fatigue and
shortness of breath), but in addition, the breakdown of red cells leads to
jaundice and increases the risk of particular long-term complications, such as
gallstones and
pulmonary hypertension.[
citation needed]Contents
Signs and symptoms
In general, signs of anemia (
pallor, fatigue, shortness of breath, and potential for
heart failure) are present. In small children,
failure to thrive may occur in any form of anemia. Certain aspects of the medical history can suggest a cause for hemolysis, such as
drugs, consumption of
fava beans due to
Favism, the presence of
prosthetic heart valve, or other medical illness.
Chronic hemolysis leads to an increased excretion of bilirubin into the
biliary tract, which in turn may lead to gallstones. The continuous release of free
hemoglobin has been linked with the development of pulmonary hypertension (increased pressure over the
pulmonary artery); this, in turn, leads to episodes of
syncope (fainting),
chest pain, and progressive breathlessness. Pulmonary hypertension eventually causes right ventricular heart failure, the symptoms of which are
peripheral edema (fluid accumulation in the skin of the legs) and
ascites (fluid accumulation in the abdominal cavity).
CausesMain articles:
Congenital hemolytic anemia and
Acquired hemolytic anemia
They may be classified according to the means of hemolysis, being either intrinsic in cases where the cause is related to the
red blood cell (RBC) itself, or extrinsic in cases where factors external to the RBC dominate.
[1] Intrinsic effects may include problems with RBC proteins or oxidative stress handling, whereas external factors include immune attack and microvascular angiopathies (RBCs are mechanically damaged in circulation).
Intrinsic causes
Hereditary (inherited) hemolytic anemia can be due to :
Extrinsic causes
Acquired hemolytic anemia may be caused by immune-mediated causes, drugs and other miscellaneous causes.
- Immune-mediated causes could include transient factors as in Mycoplasma pneumoniae infection (cold agglutinin disease) or permanent factors as in autoimmune diseases like autoimmune hemolytic anemia (itself more common in diseases such as systemic lupus erythematosus, rheumatoid arthritis, Hodgkin's lymphoma, and chronic lymphocytic leukemia).
- Paroxysmal nocturnal hemoglobinuria (PNH), sometimes referred to as Marchiafava-Micheli syndrome, is a rare, acquired, potentially life-threatening disease of the blood characterized by complement-induced intravascular hemolytic anemia.
- Any of the causes of hypersplenism (increased activity of the spleen), such as portal hypertension.
- Acquired hemolytic anemia is also encountered in burns and as a result of certain infections.
- Lead poisoning resulting from the environment causes non-immune hemolytic anemia.
- Runners can suffer hemolytic anemia due to "footstrike hemolysis", owing to the destruction of red blood cells in feet at foot impact.[2][3]
- Low-grade hemolytic anemia occurs in 70% of prosthetic heart valve recipients, and severe hemolytic anemia occurs in 3%.[4]
Mechanism
Hemolytic anemia involves the following:
- Abnormal and accelerated destruction of red cells and, in some anemias, their precursors
- Increased breakdown of hemoglobin, which may result in:
- increased bilirubin level (mainly indirect-reacting) with jaundice
- increased fecal and urinary urobilinogen
- Hemoglobinemia, methemalbuminemia, hemoglobinuria and hemosiderinuria (where there is significant intravascular hemolysis).
- Bone marrow compensatory reaction:
- Erythroid hyperplasia with accelerated production of red cells, reflected by reticulocytosis, and slight macrocytosis in peripheral blood
- Expansion of bone marrow in infants and children with severe chronic hemolysis - changes in bone configuration visible on X-ray
- The balance between red cell destruction and marrow compensation determines the severity of anemias.
In a healthy person, a red blood cell survives 90 to 120 days in the circulation, so about 1% of human red blood cells break down each day[
citation needed]. The
spleen (part of the
reticulo-endothelial system) is the main organ that removes old and damaged RBCs from the circulation. In healthy individuals, the breakdown and removal of RBCs from the circulation is matched by the production of new RBCs in the
bone marrow.
In conditions where the rate of RBC breakdown is increased, the body initially compensates by producing more RBCs; however, breakdown of RBCs can exceed the rate that the body can make RBCs, and so anemia can develop.
Bilirubin, a breakdown product of hemoglobin, can accumulate in the blood, causing
jaundice.
In general, hemolytic anemia occurs as a modification of the RBC life cycle. That is, instead of being collected at the end of its useful life and disposed of normally, the RBC disintegrates in a manner allowing free iron-containing molecules to reach the blood. With their complete lack of mitochondria, RBCs rely on glycolysis for the materials needed to reduce oxidative damage. Any limitations of glycolysis can result in more susceptibility to oxidative damage and a short or abnormal lifecycle. If the cell is unable to signal to the reticuloendothelial phagocytes by externalizing phosphatidylserine, it is likely to lyse through uncontrolled means.
[5][6][7] Dogs and cats differ slightly from humans in some details of their RBC composition and have altered susceptibility to damage, notably, increased susceptibility to oxidative damage from onion or garlic.
[8][9][10][11][12][13][14][15][16][17]
The distinguishing feature of intravascular hemolysis is the release of RBC contents into the blood stream. The metabolism and elimination of these products, largely iron-containing compounds capable of doing damage through
Fenton reactions, is an important part of the condition. Several reference texts exist on the elimination pathways, for example.
[18][19] Free hemoglobin can bind to
haptoglobin, or it may oxidize and release the heme group that is able to bind to either albumin or hemopexin. The heme is ultimately converted to bilirubin and removed in stool and urine.
[18] Hemoglobin may be cleared directly by the kidneys resulting in fast clearance of free hemoglobin but causing the continued loss of hemosiderin loaded renal tubular cells for many days.
Additional effects of free hemoglobin seem to be due to specific reactions with NO.
[20]
Diagnosis
The diagnosis of hemolytic anemia can be suspected on the basis of a constellation of symptoms and is largely based on examination of a
peripheral blood smear and a number of laboratory studies. Symptoms of hemolytic anemia include those that can occur in all anemias as well as the specific consequences of hemolysis. All anemias can cause fatigue, shortness of breath, decreased ability to exercise when severe. Symptoms specifically related to hemolysis include
jaundice and dark colored urine due to the presence of
hemoglobin (hemaglobinuria). When restricted to the morning hemaglobinuria may suggest
paroxysmal nocturnal haemoglobinuria. Direct examination of blood under a microscope in a
peripheral blood smear may demonstrate red blood cell fragments called
schistocytes, red blood cells that look like spheres (
spherocytes), and/or red blood cells missing small pieces (
bite cells). An increased number of newly made red blood cells (
reticulocytes) may also be a sign of
bone marrow compensation for anemia. Laboratory studies commonly used to investigate hemolytic anemia include blood tests for breakdown products of red blood cells,
bilirubin and
lactate dehydrogenase, a test for the free hemoglobin binding protein
haptoglobin, and the direct
Coombs test to evaluate
antibody binding to red blood cells suggesting
autoimmune hemolytic anemia.
Types of Hemolytic AnemiaThere are many types of hemolytic anemia. The condition can be inherited or acquired. "Inherited" means your parents passed the gene for the condition on to you. "Acquired" means you aren't born with the condition, but you develop it.
Inherited Hemolytic Anemias
With inherited hemolytic anemias, one or more of the genes that control red blood cell production are faulty. This can lead to problems with the hemoglobin, cell membrane, or enzymes that maintain healthy red blood cells.
The abnormal cells may be fragile and break down while moving through the bloodstream. If this happens, an organ called the spleen may remove the cell debris from the bloodstream.
Sickle Cell Anemia
Sickle cell anemia is a serious, inherited disease. In this disease, the body makes abnormal hemoglobin. This causes the red blood cells to have a sickle, or crescent, shape.
Sickle cells don't last as long as healthy red blood cells. They usually die after only about 10 to 20 days. The bone marrow can't make new red blood cells fast enough to replace the dying ones.
In the United States, sickle cell anemia mainly affects African Americans.
Thalassemias
Thalassemias (thal-a-SE-me-ahs) are inherited blood disorders in which the body doesn't make enough of certain types of hemoglobin. This causes the body to make fewer healthy red blood cells than normal.
Thalassemias most often affect people of Southeast Asian, Indian, Chinese, Filipino, Mediterranean, or African origin or descent.
Hereditary Spherocytosis
In this condition, a defect in the surface membrane (the outer covering) of red blood cells causes them to have a sphere, or ball-like, shape. These blood cells have a lifespan that's shorter than normal.
Hereditary spherocytosis (SFER-o-si-to-sis) is the most common cause of hemolytic anemia among people of Northern European descent.
Hereditary Elliptocytosis (Ovalocytosis)
Like hereditary spherocytosis, this condition also involves a problem with the cell membrane. In this condition, the red blood cells are elliptic (oval) in shape. They aren't as flexible as normal red blood cells, and they have a shorter lifespan.
Glucose-6-Phosphate Dehydrogenase (G6PD) Deficiency
In G6PD deficiency, the red blood cells are missing an important enzyme called G6PD. G6PD is part of the normal chemistry inside red blood cells.
In G6PD deficiency, if red blood cells come into contact with certain substances in the bloodstream, the missing enzyme causes the cells to rupture (burst) and die.
Many factors can trigger the breakdown of the red blood cells. Examples include taking sulfa or antimalarial medicines; being exposed to naphthalene, a substance found in some moth balls; eating fava beans; or having an infection.
G6PD deficiency mostly affects males of African or Mediterranean descent. In the United States, the condition is more common among African Americans than Caucasians.
Pyruvate Kinase Deficiency
In this condition, the body is missing an enzyme called pyruvate (PI-ru-vate) kinase. Not having enough of this enzyme causes red blood cells to break down easily.
This disorder is more common among the Amish than other groups.
Acquired Hemolytic Anemias
With acquired hemolytic anemias, your red blood cells may be normal. However, some other disease or factor causes the body to destroy red blood cells and remove them from the bloodstream.
The destruction of the red blood cells occurs in the bloodstream or, more commonly, in the spleen.
Immune Hemolytic Anemia
In immune hemolytic anemia, your immune system destroys your red blood cells. The three main types of immune hemolytic anemia are autoimmune, alloimmune, and drug-induced.
Autoimmune hemolytic anemia (AIHA). In this condition, your immune system makes antibodies (proteins) that attack your red blood cells. Why this happens isn't known.
AIHA accounts for half of all cases of hemolytic anemia. AIHA may come on very quickly and become serious.
Having certain diseases or infections can raise your risk for AIHA. Examples include:
- Autoimmune diseases, such as lupus
- Chronic lymphocytic leukemia
- Non-Hodgkin's lymphoma and other blood cancers
- Epstein-Barr virus
- Cytomegalovirus
- Mycoplasma pneumonia
- Hepatitis
- HIV
AIHA also can develop after you have a
blood and marrow stem cell transplant.
In some types of AIHA, the antibodies made by the body are called warm antibodies. This means they're active (that is, they destroy red blood cells) at warm temperatures, such as body temperature.
In other types of AIHA, the body makes cold-reactive antibodies. These antibodies are active at cold temperatures.
Cold-reactive antibodies can become active when parts of the body, such as the hands or feet, are exposed to temperatures lower than 32 to 50 degrees Fahrenheit (0 to 10 degrees Celsius).
Warm antibody AIHA is more common than cold antibody AIHA.
Alloimmune hemolytic anemia. This type of hemolytic anemia occurs if your body makes antibodies against red blood cells that you get from a
blood transfusion. This can happen if the transfused blood is a different blood type than your blood.
This type of hemolytic anemia also can occur during pregnancy if a woman has
Rh-negative blood and her baby has Rh-positive blood. "Rh-negative" and "Rh-positive" refer to whether your blood has Rh factor. Rh factor is a protein on red blood cells.
For more information, go to the Health Topic
Rh Incompatibility article.
Drug-induced hemolytic anemia. Certain medicines can cause a reaction that develops into hemolytic anemia. Some medicines, such as penicillin, bind to red blood cell surfaces and can cause antibodies to develop.
Other medicines cause hemolytic anemia in other ways. Examples of these medicines include chemotherapy, acetaminophen, quinine and antimalarial medicines, anti-inflammatory medicines, and levodopa.
Mechanical Hemolytic Anemias
Physical damage to red blood cell membranes can cause them to break down faster than normal. Damage may be due to:
- Changes in the small blood vessels.
- An artificial heart valve or other device used in blood vessels.
- Hemodialysis (HE-mo-di-AL-ih-sis). This treatment for kidney failure removes waste products from the blood.
- A heart-lung bypass machine, which may be used during open-heart surgery.
- Preeclampsia (pre-e-KLAMP-se-ah) or eclampsia. Preeclampsia is high blood pressure during pregnancy. Eclampsia, which follows preeclampsia, is a serious condition that causes seizures in pregnant women.
- Malignant hypertension (hi-per-TEN-shun). This is a condition in which your blood pressure suddenly and rapidly rises.
- Thrombotic thrombocytopenic purpura (throm-BOT-ik throm-bo-cy-toe-PEE-nick PURR-purr-ah). This rare blood disorder causes blood clots to form in small blood vessels throughout the body.
Blood cell damage also may occur in the limbs as a result of doing strenuous activities, such as taking part in marathons.
Paroxysmal Nocturnal Hemoglobinuria
Paroxysmal nocturnal hemoglobinuria (HE-mo-GLO-bih-NYU-re-ah), or PNH, is a disorder in which the red blood cells are faulty due to a lack of certain proteins. The body destroys these cells more quickly than normal.
People who have PNH are at increased risk for blood clots in the veins and low levels of white blood cells and platelets.
Other Causes of Damage to Red Blood Cells
Certain infections and substances also can damage red blood cells and lead to hemolytic anemia. Examples include malaria and blackwater fever, tick-borne diseases, snake venom, and toxic chemicals.
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