Sickle Cell Trait

A person with sickle cell trait (SCT) carries the sickle mutation in one of their two copies of the beta globin gene. This means they don’t have sickle cell disease (SCD) but they are a carrier. Both of their beta globin genes would need to have mutations to have SCD. Sickle cell trait is estimated to affect 1 to 3 million Americans and 8% to 10% of African Americans. Hispanics, South Asians, and people from Middle Eastern countries may also have SCT. More than 100 million people worldwide have SCT.

 

Unlike sickle cell disease, a serious illness in which patients have two genes that cause the production of abnormal hemoglobin (the protein in red blood cells that helps carry oxygen), people with SCT 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 SCT. Emerging research also indicates that people with SCT may have greater risk for developing chronic kidney disease.

 

Sickle cell trait can never become sickle cell disease. However, if both parents have SCT their child has a 25% chance of having sickle cell disease. If only one parent has SCT, their child has a 50% chance of also inheriting it, but they cannot get sickle cell disease as well. This is why it’s important to know your partner’s trait status if you plan to have children.

Signs and Symptoms

Most people with sickle cell trait have no symptoms and will not have any health complications. Rarely, people with SCT can have blood in their urine. This should be brought to a medical provider’s attention, as it can be a sign of a very rare form of kidney cancer (renal medullary carcinoma) that is associated with SCT. Under extreme conditions such as high altitude, severe dehydration, or very high intensity physical activity, SCT red blood 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.

Risk Factors

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

  • African Americans (8% to 10% have sickle cell trait)
  • Hispanics
  • South Asians
  • People from Middle Eastern countries

All newborns in the U.S. are now tested for sickle cell disease and sickle cell trait. SCD 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 January 2025, ASH issued an updated position statement listing "sickle cell crisis" or "sickle cell trait" as a cause of death on an autopsy report for an individual with SCT is medically inaccurate and without medical evidence of causation.

Is it Considered Safe to Play Sports if I Have Sickle Cell Trait?

When taking normal precautions, it is considered safe for people with sickle cell trait to play sports and engage in moderate exercise. SCT — when a person carries a single gene for sickle cell disease — is not an illness, and most people with this trait will lead normal, active, and healthy lives without any associated symptoms or health conditions. In fact, several professional athletes are carriers of the trait.

Under extreme circumstances, there is a risk of a rare muscle injury. This breakdown of muscle (rhabdomyolysis) was found in people with SCT who have participated in high-intensity exercise, such as military training, and can lead to kidney failure and death. Rather than exclude people with SCT from military service, basic training procedures were reviewed and modified to make it safe for everyone. Rhabdomyolysis can affect anyone in extreme circumstances including high altitude, intense heat, or a crush injury.

Take breaks and stay hydrated. ASH developed a policy with several associations to urge athletic organizations to adopt universal preventive measures in their training programs to protect all athletes, regardless of SCT status, from illness and death related to high-intensity exercise. Ensuring proper water intake and rest breaks was part of that policy.

Blood Health Information Hub

Find additional trustworthy information on blood disorders in the full Blood Health Information Hub library. Have you seen any misinformation on blood disorders you want ASH to address? Contact bloodhealthinfohub@hematology.org.

ASH Center for Sickle Cell Disease Initiatives

Learn how ASH is driving change in SCD treatment through research and care initiatives. It aims to enhance this commitment and streamline its programs for greater impact, ensuring sustainable improvements for those affected by SCD.

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