Sickle cell trait is a genetic feature that affects the blood. Usually, a person who has it has no symptoms, but they may need to take a few extra precautions. It is different from sickle cell disease.

In medical terms, a trait is an inherited feature. A person with sickle cell trait (SCT) has inherited one atypical hemoglobin gene from one biological parent and another gene without this characteristic from the other. Hemoglobin is a protein in red blood cells that carries oxygen around the body.

SCT is an inherited disorder that affects red blood cells. It occurs in 1–3 million individuals in the United States.

In this article, learn what SCT is and what it means for the people who have it.

Athlete running after SCT trainingShare on Pinterest
Athletes with sickle cell trait may need to take precautions during training.

People with SCT have inherited one gene for typical hemoglobin and one for sickle cell hemoglobin. Inheriting only one of the genes that causes it is what makes sickle cell trait different from sickle cell disease.

In the U.S., SCT is most common among African Americans, affecting 8–10% of these individuals. It also occurs in other ethnicities, including Hispanic Americans from Central and South America and people of southern Europe, Middle Eastern, Asian, Indian, and Mediterranean descent.

Sickle cell disease occurs when a person inherits two sickle cell genes — one from each biological parent. This makes red blood cells hard, sticky, and shaped similar to sickles.

Sickle-shaped cells die quickly, so people with the disease have a shortage of red blood cells. These sickle-shaped cells can also clog smaller blood vessels and cause serious health issues.

Most people with SCT have no medical issues as a result — the trait cannot develop into the disease.

While symptoms are rare, they can include blood in the urine or general pain and discomfort. Circumstances that can trigger the symptoms include:

  • being at high altitudes, such as when flying or mountain climbing
  • performing intense exercise, especially if it leads to dehydration
  • being in environments at high pressure, such as when scuba diving

Under a microscope, the blood cells of a person with SCT usually appear routine. However, when there is oxidative stress, they adopt a sickle-like shape.

Most individuals with SCT experience no complications, though these can develop under extreme circumstances.

Additionally, people with SCT may be more likely to experience the following health issues:

There is also a higher risk of sudden death due to exertion.

While most experts consider SCT to be benign, there is some debate about the rates of various complications.

Some researchers have called for greater awareness of the condition and more emphasis on screening and genetic counseling.

Meanwhile, more funding is necessary for research and awareness of sickle cell disease worldwide. In the U.S., this area of health receives less funding than toward cystic fibrosis, for example, which affects fewer people.

The lack of funding for SCT and sickle cell disease stems from inequity in healthcare, a problem that health experts state needs urgent addressing.

It is possible to pass on SCT to children. Also, when both biological parents have this trait, they may have a child with sickle cell disease.

For this reason, it is crucial to understand how the trait passes on and how likely people can inherit the feature.

If both biological parents have SCT, there is:

  • a 50% chance their child will have the trait
  • a 25% chance their child will have sickle cell disease
  • a 25% chance their child will have neither the trait nor the disease

However, if only one biological parent has SCT, there is a 50% chance their child will have it.

Anyone with concerns about the chances of passing on the trait should discuss the implications and testing options with a doctor.

Since sickle cell disease symptoms can start as early as 5 months of age, so early diagnosis is critical. Therefore, it is now routine in the U.S. to test all newborns.

Typically, approximately 1 in 13 Black or African American babies are born with SCT. And sickle cell disorder can develop in 1 out of every 365 Black or African American births. It can also occur in about 1 in every 16,300 Hispanic American births.

For older children and adults, a doctor can diagnose SCT with a blood test. This involves taking a blood sample from the end of the finger or a vein in the arm and sending it to a laboratory for analysis.

Insurance often covers testing for SCT. Screening is also routine for athletes and people joining the military.

SCT usually requires no treatment, as most people do not experience any symptoms.

However, a person may wish to consult a doctor if they know they have the trait and are planning to:

  • have children
  • be an athlete
  • join the military

Considerations during extreme exercise

People with SCT are more likely to have muscle breakdown or heatstroke when engaging in intense physical exercise, such as competitive sports or military training.

Therefore, it is crucial to avoid getting overheated and dehydrated during physical activity. Tips include:

  • building up the intensity of workouts slowly
  • resting between sets and drills
  • drinking plenty of water before, during, and after activity
  • keeping cool by misting with water or going to an air-conditioned area during breaks
  • receiving medical care immediately if any symptoms of illness develop

Considerations during pregnancy

If a person knows that they have SCT, they can speak with a genetic counselor before having children.

The counselor will look at the family histories of the individual and their partner and discuss any relevant risks and considerations.

SCT is a genetic feature. Most people who have it experience no symptoms, but there is a higher risk of certain complications, so taking precautions may be necessary, such as during extreme exercise.

A person can pass the trait on, and if both biological parents have the trait, their child may have sickle cell disease, a different issue that can be serious.

For this reason, health experts recommend that anyone with SCT speak with a genetic counselor before having children.