Sickle cell trait (SCT) is an inherited blood disorder. It affects 1 to 3 million Americans. The numbers vary based on race and nationality. For example, the American Society of Hematology estimates that 8 to 10 percent of Black people have the trait. It’s also seen in Hispanic people, South Asians, people of Southern European descent, and people from the Middle East.

A person with SCT has inherited only one copy of the sickle cell gene from a parent. A person with sickle cell disease (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 sickle cell disease. 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 sickle cell disease.

Sickle cell disease

Sickle cell disease affects the red blood cells. People with SCD have defective hemoglobin, the oxygen-carrying component of red blood cells. 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 behave as they should, transporting oxygen-rich blood to the tissues and organs in the body.

Sickle cell trait is passed on from parent to child. If both parents have SCT, their biological children have a 50 percent chance of having SCT and a 25 percent chance of having the more serious sickle cell disease. If just one parent has sickle cell trait, their children have a 50 percent chance of inheriting SCT, but do not have any chance of developing SCD.

Unlike the more serious sickle cell disease, 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 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 sickle cell disease 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.

If you’re concerned that SCT may run in your family, your doctor or local health department can perform a simple blood test. All babies born in a hospital in the United States are tested for sickle cell disease and sickle cell trait.

SCT is typically a fairly benign disorder. Under certain conditions, it can be harmful. In a study published in the New England Journal of Medicine, army recruits with SCT who were put through rigorous physical training had 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, researchers found that Black people with SCT had a two-fold increased risk of developing a blood clot in their lungs compared with Black men without the trait. Blood clots can become life-threatening when they cut off the oxygen supply to the lung, heart, or brain.

Sickle cell trait is a common disorder, especially among Black people. It generally presents no problems unless the faces extreme physical conditions. For this reason, and because of its high likelihood of being passed on, you should talk to your doctor about being tested and monitored for the condition if you’re in a high-risk group. High-risk groups include Black people and people of Hispanic, South Asian, Southern European, or Middle Eastern decent. Being monitored is especially important if you’re a known carrier and an athlete, or if you’re thinking of starting a family.