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Sickle Cell Trait

Sickle cell trait is an inherited blood disorder that affects 1 million to 3 million Americans and 8 to 10 percent of African Americans. Sickle cell trait can also affect Hispanics, South Asians, Caucasians from southern Europe, and people from Middle Eastern countries. More than 100 million people worldwide have sickle cell trait.

Unlike sickle cell disease, a serious illness in which patients have two genes that cause the production of abnormal hemoglobin (the substance in red blood cells that helps carry oxygen), individuals with sickle cell trait carry only one defective gene and typically live normal lives. Rarely, extreme conditions such as severe dehydration and high-intensity physical activity can lead to serious health issues, including sudden death, for individuals with sickle cell trait.

If an individual has sickle cell trait, it means that he or she carries or has inherited a single copy of the gene that causes sickle cell disease. It is not a disease. In general, people with sickle cell trait enjoy normal life spans with no medical problems related to sickle cell trait.

Sickle cell trait can never become sickle cell disease. It is possible, however, for individuals with sickle cell trait to pass the gene to their children. 

Signs and Symptoms

Most people with sickle cell trait have no symptoms and will not have any health complications. Occasionally people with sickle cell trait can have blood in their urine. Under extreme conditions such as high altitude, severe dehydration, or very high intensity physical activity, red cells can become deformed or sickled. Complications include muscle breakdown (rhabdomyolysis), reduced blood supply to the spleen (ischemia/infarction), or increased pressure in the eye (glaucoma) following eye injuries. Finally, a very rare form of kidney cancer (renal medullary carcinoma) has been associated with sickle cell trait.

Risk Factors

Sickle cell trait is more common in certain ethnic groups, including:

  • African Americans (8 to 10 percent of African Americans have sickle cell trait)
  • Hispanics
  • South Asians
  • Caucasians from southern Europe
  • People from Middle Eastern countries

All newborns in the United States are now tested for sickle cell disease and sickle cell trait. Sickle cell disease can be identified before birth by testing a sample of amniotic fluid or tissue from the placenta. People who carry the sickle cell gene can seek genetic counseling before pregnancy to discuss options.

ASH Position on Sickle Cell Trait as a Cause of Death

In May 2021, ASH issued an updated position statement asserting that it is medically inaccurate to claim sickle cell trait as a cause of death based solely on the presence of sickled cells at autopsy. ASH’s policy was updated in response to the recent investigation and coverage in The New York Times, How a Genetic Trait in Black People Can Give the Police Cover. ASH President, Martin Tallman, MD, also issued this statement and submitted a letter to the editor that was published online in The New York Times on May 25, 2021.

Sickle Cell Trait and Athletic Participation

Individuals can and do lead active lifestyles. In fact, several professional athletes are carriers of the trait. In recent years, however, there has been heightened attention on cases of athletes with sickle cell trait who have experienced exertion-related illness and, in some cases, sudden death, during or after strenuous athletic training sessions. These cases caused some organizations to mandate that athletes be tested for sickle cell trait as a prerequisite to participation and has led to some confusion about whether or not it is safe for individuals with sickle cell trait to play sports.

In January 2012, ASH released a Policy Statement on Screening for Sickle Cell Trait and Athletic Participation, opposing mandatory sickle cell trait screening as a prerequisite to athletic participation and urging athletics programs to adopt universal preventive interventions in their training programs to protect all athletes from exertion-related illness and death. These preventative interventions include drinking adequate amounts of fluid and taking rest breaks as needed, as well as having staff present at organized sport practices or games who can recognize when a participant may be experiencing exertion related complications and may need medical attention. The policy statement also states that screening for sickle cell trait should be voluntary and should take place in a setting that ensures privacy and is performed by a knowledgeable provider who is able to offer comprehensive counseling.

Access a list of frequently asked questions about sickle cell trait.