Sickle Cell Disease

What is sickle cell disease?
Sickle cell disease is an inherited condition affecting the red blood cells. Hemoglobin, a protein in red blood cells, is responsible for transporting oxygen to all parts of the body. Normal red blood cells with normal hemoglobin pass easily through the blood vessels because of their flexible, round shape. When a person has sickle cell disease, the hemoglobin is altered, causing the entire red blood cell to take on a more rigid, sickle shape. Sickle-shaped red blood cells cannot pass easily through the circulatory system and may cause blood vessels to become clogged. When a vessel is clogged, blood flow to the tissues may be impaired and tissue damage may result. Also, as the sickle cells are trapped and destroyed, there are not enough functioning red blood cells, resulting in anemia.²

What are the complications of sickle cell disease?

• Anemia: This condition is caused by a shortage of red blood cells to carry oxygen to the body's tissues. Individuals with anemia may have decreased energy.²
• Painful episodes: When red blood cells block the flow of blood to tissues, an individual may experience pain in that area.^1,2
• Splenic sequestration crisis: The spleen may enlarge rapidly due to trapped red blood cells.³
• Infections: Infections are the leading cause of death in children with sickle cell disease.²
• Aplastic crisis: This condition occurs during the time the body does not make red blood cells.³
• Stroke: A stroke may occur due to blockage of blood vessels in the brain.¹

Who is at risk for sickle cell disease?
Sickle cell disease is inherited in a recessive manner. Each parent must be a carrier of the sickle cell trait (or gene) to have an affected child. If both parents are carriers of the sickle cell gene, there is a 25% chance with each pregnancy of having an affected child.² Sickle cell disease is more common in certain populations.

The following table lists the carrier frequency based on ancestry.⁴

It is recommended that individuals of African, Caribbean, and Hispanic ancestry consider carrier testing for the sickle cell trait. Any individual with a family history of the sickle cell trait or disease should also consider carrier testing. ²

What laboratory tests are available?

• Hemoglobin electrophoresis
  In many cases, a hemoglobin electrophoresis can provide diagnostic information about the sickle status of a patient. A hemoglobin electrophoresis is a blood test that can determine the percentage of different types of hemoglobin in a person's blood. A hemoglobin electrophoresis test can distinguish an individual with a sickle cell disease from one who is a sickle cell carrier. Many, but not all, abnormal types of hemoglobin will be detected by a hemoglobin electrophoresis.^1,2
• Sickle Prep test
  The sickle prep test is a blood smear on a slide. By looking through a microscope, sickle-like red blood cells can be identified. A sickle prep test will not rule out other types of abnormal hemoglobin. The sickle prep test is not recommended for infants younger than 12 months of age.³
• Hemoglobin Solubility test
  The hemoglobin solubility test (also called SickleDex) is a blood test that can determine whether a person has sickle hemoglobin. However, this test cannot distinguish an individual with sickle cell disease from an individual who is a sickle cell carrier. Hemoglobin solubility testing is not recommended for infants younger than 12 months of age. A hemoglobin solubility test cannot rule out or diagnose other types of abnormal hemoglobin.³
• DNA testing
  If a fetus is at risk for sickle cell disease, prenatal direct DNA testing is available on amniotic fluid or CVS samples.⁴ DNA tests are sometimes ordered in other clinical situations to confirm carrier or affected status.

Amniocentesis | CVS

More information about sickle cell disease is available at http://www.sicklecelldisease.org/

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References

1. Sickle Cell Disease Association of America. What is Sickle Cell Disease? Culver City, Ca: SCDAA; www.sicklecelldisease.org/about_scd/index.phtml [cited March 25, 2005].
2. March of Dimes Birth Defects Foundation. March of Dimes Public Health Education Information Sheet Sickle Cell Disease. White Plains, NY: 1992.
3. National Institute of Heart, Lung and Blood Institute. Management and Therapy of Sickle Cell Disease. Bethesda, Md: National Institutes of Health; 1995. [NIH publication 96-2117].
4. Ashley-Koch A, Yang Q, Olney RS. Hemoglobin S Allele and Sickle Cell Disease. Centers for Disease Control. HuGE Review; Atlanta, Ga: 1998. www.cdc.gov/genetics/hugenet/reviews/sickle.htm [cited August 25, 2000].

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