Sickle cell anemia is an inherited form of anemia, a disease typically diagnosed at birth or soon after, in which not enough healthy red blood cells are produced to carry sufficient oxygen throughout the body.
Sickle cell anemia is caused by a mutation in the HBB gene that leads to the production of abnormal hemoglobin — the protein that carries oxygen in the blood. Abnormal hemoglobin causes red blood cells to be misshapen, rigid and sticky. This makes it harder for the cells to move through small blood vessels, impairing circulation and causing blockages.
All individuals have two copies of each gene, one inherited from each parent. People who inherit only one mutated copy of the HBB gene generally do not show any symptoms of sickle cell anemia, and are said to have sickle cell trait. However, those with two faulty copies of the gene — one from each parent — will develop sickle cell anemia.
Screening and testing
Screening for sickle cell anemia is done with a simple blood test that detects the presence of the abnormal hemoglobin protein. In many countries, including the United States and Great Britain, this blood test is part of a routine newborn screening.
Adults can also receive the test if they are concerned they might have sickle cell trait. Sickle cell anemia is most common among people of African descent, but can also be found in those of Hispanic, Southern European, Middle Eastern or Asian descent.
Patients who test positive for abnormal hemoglobin do not necessarily have sickle cell anemia and may only have sickle cell trait. For this reason, further testing is needed to make a definite diagnosis. A blood test may also be repeated to rule out a false positive result.
Several types of sickle cell anemia exist, depending on which type of abnormal hemoglobin the patient’s body makes. These vary in the severity of symptoms. A second, more specific blood test is used to determine which type of abnormal hemoglobin a patient produces.
A test for sickle cell anemia may also be performed before birth using a small sample of amniotic fluid or the placenta. These tests screen for the mutated HBB gene rather than abnormal hemoglobin protein.
Patients diagnosed with sickle cell anemia require frequent laboratory tests including blood and urine tests, in order to monitor them for complications like kidney problems or infections. Patients may also receive a transcranial Doppler ultrasound screening (TCD) — a painless procedure that uses sound waves to examine blood flow in the brain. It lets doctors assess the risk of stroke, and start treatments to reduce that risk if necessary.
Patients with sickle cell trait or parents of newborn babies diagnosed with sickle cell anemia or sickle cell trait are often referred to genetic counseling. This helps prospective parents determine the probability of future children inheriting the disease, and helps them make fully informed reproductive decisions.
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