A form of anaemia (a reduced level of the oxygen-carrying pigment haemoglobin in the blood) caused by premature destruction of red blood cells in the bloodstream (see haemolysis). The bone marrow has the capacity to increase its red cell production approximately sixfold over normal rates. Haemolytic anaemia will result only if the shortening of the lifespan of red blood cells is sufficiently severe to overcome the reserve capacity of the bone marrow.
Haemolytic anemias can be classified into two categories: those caused by abnormalities within the red blood cells themselves, which are typically inherited conditions, and those caused by factors external to the cells, which are typically acquired later in life.
When haemolysis is attributed to an abnormality within the red blood cells, it often stems from an irregular rigidity of the cell membrane, the thin layer enveloping each cell. This rigidity causes the cells to become trapped in the small blood vessels of the spleen during the early stages of their lifespan, where they are subsequently eliminated by macrophages, specialized cells responsible for engulfing foreign particles. The abnormal rigidity may arise from an inherited defect of the cell membrane, such as in the case of hereditary spherocytosis, or from a defect in the hemoglobin within the cell, as observed in sickle cell anemia. Furthermore, defects in one of the cell’s enzymes can also contribute to this rigidity. Inherited deficiency of the glucose-6-phosphate dehydrogenase (G6PD) enzyme can lead to episodes of haemolytic anemia, as the red blood cells become prone to damage during infections, certain medications, or specific dietary choices. One particular form of G6PD deficiency is most prevalent in Mediterranean countries.
Haemolytic anemias resulting from defects external to the red blood cells can be categorized into three primary groups. The first group consists of disorders where red cells are destroyed due to mechanical forces like friction caused by artificial surfaces (e.g., replacement heart valves), abnormal linings of blood vessels, or the presence of blood clots within vessels. The second group comprises immune-mediated haemolytic anemias, which can occur when foreign blood cells enter the bloodstream (such as in an incompatible blood transfusion) or due to autoimmune disorders where the immune system mistakenly attacks the body’s own tissues. Haemolytic disease of the newborn is a specific example within this group, where the baby’s red cells are destroyed by antibodies produced by the mother and transferred across the placenta. The third group involves the destruction of red blood cells by microorganisms within the bloodstream, with malaria being the most common cause of such destruction.
Individuals with haemolytic anemia may experience symptoms commonly associated with all types of anemia, including fatigue and breathlessness. Additionally, they may also exhibit symptoms specific to haemolysis, such as jaundice. Jaundice occurs as a result of an elevated concentration of bile pigments in the blood, which are formed due to the destruction of red blood cells.
Diagnosis of haemolytic anemias is confirmed through microscopic examination of the blood. Treatment approaches depend on the underlying cause. In some cases of inherited anemias, the removal of the spleen can help in managing the condition. For other types, such as G6PD deficiency and favism, prevention involves avoiding drugs or foods that can trigger hemolysis. Immune-mediated anemias can often be controlled with the use of immunosuppressant drugs. In situations where there is a life-threatening anemia, emergency treatment may involve transfusions of red blood cells.