Anaemia

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Haemolytic Anaemias

Rarely, anaemia is due to problems that cause the red blood cells (RBCs) to die or be destroyed early in their life. Normally, red cells live in the blood for about 4 months. In haemolytic anaemia, 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 reduced ability to carry oxygen to all parts of the body. This results in the typical symptoms of anaemia including:

  • weakness and/or tireness
  • lack of energy

Depending on its cause, haemolytic anaemia can be chronic, developing and lasting over a long period or lifetime, or may be acute, occurring very rapidly with the development of serious signs and symptoms. The various forms of haemolytic anaemia can have a wide range of signs and symptoms.

The different causes of haemolytic anaemia fall into two main categories:

  • Inherited forms in which a gene or genes are passed from one generation to the next and result in abnormal RBCs or haemoglobin
  • Acquired forms in which something other that inherited disease results in the early destruction of RBCs

Inherited Haemolytic Anaemia
Two of the most common causes of inherited haemolytic anaemia are sickle cell anaemia and thalassaemia:

Sickle cell anaemia, due to production of an abnormal form of haemoglobin called HbS, usually causes no difficulties as the “trait” (when you carry only one mutated gene from one of your parents), but severe clinical problems as the “disease” (when you carry two mutated genes, one from each of your parents). The red blood cells are misshapen, unstable (leading to haemolysis) and can block blood vessels, causing pain and anaemia. Screening is usually done on newborns – particularly those of African descent. Sometimes screening is done prenatally on a sample of amniotic fluid. Follow up tests for haemoglobin variants may be performed to confirm a diagnosis. Treatment is usually based on the type, frequency and severity of symptoms.

Thalassaemia is a hereditary abnormality of haemoglobin production and results in small red blood cells that resemble those seen in iron deficiency. In its most severe form, the red cells have a shortened life span. In milder forms, anaemia is usually mild or absent, and the disease may be detected by finding small blood cells on a routine FBC.

This genetic disease is found frequently in people of Mediterranean, African, and Asian heritage. The defect in production may involve one of two components of haemoglobin called the alpha and beta protein chains. The disease is called alpha thalassaemia or beta thalassaemia accordingly. The "beta minor" form (sometimes called beta thal trait, as with sickle cell) occurs when a person inherits half normal genes and half beta thalassaemia genes. It causes a mild anaemia and no other symptoms. The "beta major" form (due to inheriting two beta thalassaemia genes and also called Cooley’s anaemia) is more severe and may result in growth problems, jaundice (yellowing of the skin and whites of the eyes), and severe anaemia.

Other less common types of inherited forms of haemolytic anaemia include:

  • Hereditary spherocytosis—a weakness in the red cell wall which results in abnormally shaped small dark rounded RBCs which may be seen on a blood film
  • Hereditary elliptocytosis—another red cell wall defect causing abnormally cigar-shaped RBCs seen on a blood film
  • Glucose-6-phospate dehydrogenase (G6PD) deficiency—G6PD is an enzyme that is necessary for RBC survival. Its 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 may also be diagnosed with a test for its activity
  • Abnormal haemoglobins (“haemoglobinopathies”) other than sickle disease – there are many of these, often extremely rare.

Laboratory Tests
Since some of these inherited forms may have mild symptoms, they may first be detected on a routine FBC and blood film 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:

  • Tests for haemoglobin variants such as haemoglobin electrophoresis
  • DNA analysis—not routinely done but can be used to help diagnose haemoglobin variants, thalassaemia, 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 anaemia can be reduced by treatment. Sometimes these disorders may have implications for planned pregnancies, especially if both partners have abnormal types of haemoglobin, and specialist advice and sometimes further investigations may be helpful in assessing risks for future babies.

Acquired Haemolytic Anaemia
Some of the conditions or factors involved in acquired forms of haemolytic anaemia include:

  • Autoimmune haemolytic anaemia (AIHA) or cold agglutinin disease (CHAD)—conditions in which the body produces antibodies against its own red blood cells.
  • Transfusion reaction—result of blood donor-recipient incompatibility. This occurs very rarely but when it does can have some serious complications.
  • Mother-baby blood group incompatibility (especially rhesus antigen incompatibility where mothers are Rhesus-negative)—may result in haemolytic disease of the newborn.
  • Drugs—certain drugs such as penicillin can trigger the body into producing antibodies directed against RBCs or cause the direct destruction of RBCs. Other drugs, such as some antimalarial drugs and some anaethetics can cause destruction of red cells in susceptible individuals with G6PD deficiency or some forms of abnormal haemoglobin.
  • Physical destruction of RBCs by, for example, an artificial heart valve or cardiac bypass machine used during open-heart surgery
  • Paroxysmal Nocturnal Haemoglobinurina (PNH)—a rare condition in which the different types of blood cells including RBCs, WBCs and platelets may be abnormal. Because the RBCs are defective they are susceptible to destruction by the body’s immune system. As the name suggests, people with this disorder can have acute, recurring episodes in which many RBCs are destroyed. 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). Patients will often pass dark urine due to the haemoglobin 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. Episodes are thought to be brought on when the body is under stress during illnesses or after physical exertion. (For more on this, see the Genetic Home Reference webpage.)

These types of haemolytic anaemias are often first identified from signs and symptoms see during physical examination and after taking a medical history. A medical history can reveal, for example, a recent transfusion, treatment with penicillin or cardiac surgery. A FBC and/or blood film 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) (formerly known as a “Coombs’ test”) in the case of transfusion reaction, mother-baby blood type incompatibility, or autoimmune haemolytic anaemia
  • Haptoglobin – this protein mops up free haemoglobin in the blood for recycling after blood cells are haemolysed and may be reduced in the blood during periods of haemolysis.
  • Reticulocyte count – reticulocytes are young red blood cells and an increase reflects increased production of red cells in the bone marrow to keep up with haemolysis.

Treatment for haemolytic anaemia depends on the cause. Never-the-less, the goals are the same: to treat the underlying cause of the anaemia, to decrease or stop the destruction of RBCs and to increase the RBC count and/or haemoglobin level to alleviate symptoms. This may involve, for example:

  • Drugs used to decrease production of autoantibodies that destroy RBCs
  • Blood transfusions to increase number of healthy RBCs
  • Bone marrow transplant—to increase production of normal RBCs
  • Avoiding triggers that cause the anaemia such as the cold in some forms of autoimmune haemolytic anaemia or fava beans and certain drugs for those with G6PD deficiency

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