Sickle cell trait (SCT) is an inherited blood disorder. It affects 1 to 3 million Americans, according to the American Society of Hematology.

A person with SCT has inherited only one copy of the sickle cell gene from a parent. A person with SCD has two copies of the gene, one from each parent.

Because a person with SCT has only one copy of the gene, they will never develop SCD. Instead, they’re considered a carrier for the disease. That means they can pass the gene for the disease on to their children. Depending on the genetic makeup of each parent, any child can have varying chances of having SCT and developing SCD.

Sickle cell disease

SCD affects the red blood cells. People with SCD have hemoglobin, the oxygen-carrying component of red blood cells, that does not function properly. This impaired hemoglobin causes the red blood cells, which are normally flattened disks, to become crescent-shaped. The cells look like a sickle, a tool used in farming. That’s where the name comes from.

People with SCD typically also have a shortage of red blood cells. The red blood cells that are available can become inflexible and sticky, blocking the flow of blood through the body. This restriction in blood flow can cause:

  • pain
  • anemia
  • blood clots
  • low oxygen supply to tissues
  • other disorders
  • death

Sickle cell trait

On the other hand, sickle cell trait rarely leads to deformity in red blood cells, and only under certain conditions. Under most circumstances, people with SCT have enough normal hemoglobin to prevent the cells from becoming sickle-shaped. Without the sickling, red blood cells function as they should, transporting oxygen-rich blood to the tissues and organs in the body.

SCT can be passed on from parent to child. If both parents have sickle cell trait, they may have a child with the disease.

If both parents have sickle cell trait, according to the Centers for Disease Control and Prevention (CDC), there is:

  • a 50 percent chance that their child will have the trait
  • a 25 percent chance their child will have SCD
  • a 25 percent chance their child will have neither the trait nor the disease

If only one parent has sickle cell trait, there is:

  • a 50 percent chance that their child will have the trait
  • a 50 percent chance that their child will not have it

Since SCD symptoms can start as early as 5 months old and early diagnosis is critical, it is routine in the United States to test all newborns.

Unlike the more serious SCD, SCT generally causes no symptoms. Most people with the condition have no direct health consequences due to the disorder.

Some people with SCT can have blood in their urine. Because blood in the urine can be a sign of a serious condition, such as bladder cancer, it should be checked out by a medical professional.

Although it’s rare, people with SCT can develop symptoms of SCD under extreme conditions. These conditions include:

  • an increased pressure in the atmosphere, such as with scuba diving
  • low oxygen levels, which can occur while performing strenuous physical activity
  • high altitudes
  • dehydration

Athletes with SCT need to take precautions when performing. Staying hydrated is extremely important.

About 75 percent of SCD cases occur in Sub-Saharan Africa (Nigeria bearing the most occurrences), or among populations with ancestors in this region or from other parts of the world where malaria is or was common. sickle cell mutation is believed by scientists to have evolved in response to protect against malaria.

According to the CDC, the sickle cell trait can protect against malaria resulting in higher incidences of sickle cell carriers in malaria-endemic areas. In fact, scientists believe the sickle cell mutation evolved as a protective response against malaria.

According to the American Society of Hematology, in the United States, the sickle cell trait appears most often in African American population, affecting 8 to 10 percent.

However, per the CDC, it is also prevalent among individuals whose ancestors came from Spanish-speaking regions in the Western Hemisphere (South America, the Caribbean, and Central America), Saudi Arabia, India, and Mediterranean countries such as Turkey, Greece, and Italy.

Additionally, about 1 in 13 Black or African American babies are born with sickle cell trait, and sickle cell disease can be found in 1 out of every 365 Black or African American births. It is also present in about 1 out of every 16,300 Hispanic American births.

If you’re concerned that SCT may run in your family, your doctor or local health department can perform a simple blood test.

SCT is typically a fairly benign disorder. Under certain conditions, however, it can be harmful. In a study published in the New England Journal of Medicine in 2016, army recruits with SCT who were put through rigorous physical training were shown to have no greater chances of dying than recruits who didn’t have the trait.

They were, however, much more likely to have a breakdown of muscle tissue that can lead to kidney damage. In these circumstances, alcohol may also have played a role.

In another study published in the Journal of Thrombosis and Haemostasis in 2015, researchers found that Black people with SCT had a two-fold increased risk of developing a blood clot in their lungs compared with Black people without the trait. Blood clots can become life threatening when they cut off the oxygen supply to the lungs, heart, or brain.

Furthermore, the lack of access to healthcare negatively impacts individuals with SCD, leading to shorter life expectancy.

When comparing financial support for cystic fibrosis, which affects about 35,000 people in the United States annually, to that of SCD, it receives 7 to 11 times more funding per patient than SCD and more new clinical trials and new drug approvals. There’s a funding disparity even though SCD affects far more people.

Sickle cell trait is a common disorder, especially among Black people. It generally presents no problems unless the person faces extreme physical conditions. For this reason, and because of its high likelihood of being passed on, you should talk with your doctor about being tested and monitored for the condition if you’re at a higher risk for the disorder.

Those who are at increased risk include Black people and people of Hispanic, South Asian, Southern European, or Middle Eastern descent. Being monitored is especially important if you’re a known carrier and an athlete, or if you’re thinking of starting a family.