Sickle cell anemia is caused by a genetic mutation that leads to the production of abnormal hemoglobin known as sickle hemoglobin. Sickle hemoglobin binds less oxygen than normal, lowering the oxygen-carrying capacity of the blood. Sickle hemoglobin also leads to sickle-shaped red blood cells, which interfere with blood flow and increase the viscosity (thickness and stickiness) of the blood.

A blood transfusion is used to provide a person with donated blood via intravenous injection. Different blood components can be delivered through this procedure. In sickle cell anemia patients, a blood transfusion is used to provide normal red blood cells to the patient’s body. Red blood cell transfusions help against anemia and to lessen the blood’s viscosity, allowing it to flow more freely so as to easy disease symptoms and prevent complications.

Kind of blood transfusions

There are two different kinds of red blood cell transfusions: simple transfusions and exchange transfusions. Simple transfusions are used to deliver additional healthy red blood cells to the patient’s body, while exchange transfusions exchange the patient’s sickle-shaped blood cells with healthy ones — lowering the concentration of sickle cells without increasing blood viscosity.

Simple transfusions are typically given in intervals, possibly once or twice a month, to maintain a healthy proportion of normal to sickle red blood cells.

Transfusions can also be divided into acute, long-term, and short-term transfusions. Acute transfusions are given briefly before surgery, short-term transfusions are given to assist a pregnancy, and long-term transfusions are given to prevent complications such as strokes.

When is a blood transfusion recommended?

Transfusions are either performed to increase the blood’s oxygen-carrying capacity in case of severe anemia or to decrease the viscosity of the blood.

Transfusion to increase oxygen capacity

Certain situations make it crucial to increase the oxygen-carrying capacity of red blood cells in sickle cell patients. For example, an infection with parvovirus B19 can decrease erythropoiesis or the production of new red blood cells. Since sickle red blood cells already have a reduced oxygen-binding capacity and are shorter lived than normal red blood cells, such an infection can be very dangerous for these patients. In such cases, a red blood cell transfusion can be life-saving.

Sickle red blood cells can also become trapped in the blood vessels of the spleen, blocking blood flow, a complication known to occur in about 25 percent of sickle cell patients. This so-called sequestration crisis causes severe anemia and a massive enlargement of the spleen, leading to abdominal pain. A blood transfusion is crucial in a sequestration crisis, helping trapped red blood cells to move back into the circulation.

Transfusion to lower blood viscosity

In patients with a high risk of stroke, blood transfusions may help to prevent stroke and brain damage. In such cases, transfusions need to be performed regularly. One method to detect stroke risk is by transcranial Doppler ultrasound. This is a test that measures blood flow through blood vessels in the brain. A faster blood flow is associated with an increased risk of stroke.

Anemia seen in sickle cell patients can also lead to acute chest syndrome (ACS), a condition where the oxygen concentration in the blood drops below a critical level, and breathing becomes difficult. ACS is a common cause of death in sickle cell anemia patients, and an exchange transfusion is strongly recommended within 48 hours of diagnosis.

Risks associated with blood transfusions

A patient who undergoes a blood transfusion may develop antibodies against the blood they receive, a phenomenon called alloimmunization. This can cause serious complications, including hemolytic transfusion reaction, or a dangerous drop in hemoglobin levels to below those prior to the transfusion. To reduce the risk of alloimmunization, tests to match the blood group and rhesus factor of the patient are used.

A blood transfusion can also lead to an excess of iron. This can damage the heart, liver, and other organs. Iron chelators, or medicines that bind iron, can help remove the excess iron from the patient’s body.

Finally, blood transfusions carry a risk of a infection. But, blood products that are used for transfusion are carefully screened, keeping the risk of infection low.

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