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

Medically speaking, a trait is an inherited feature. A person with sickle cell trait has inherited one abnormal hemoglobin gene from one parent and one normal gene from the other. Hemoglobin is a protein in red blood cells that carries oxygen around the body.

In the United States, sickle cell trait is most common among Black people, but it can occur in people who are Latinx or from the Mediterranean region, South Asia, or the Middle East.

In this article, learn what sickle cell trait 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.

Sickle cell trait is an inherited disorder that affects red blood cells. It occurs in 1–3 million people in the U.S. and 8–10% of Black people in the country.

People with sickle cell trait have inherited one gene for normal hemoglobin and one for sickle cell hemoglobin. Inheriting only one abnormal gene is what makes sickle cell trait different from sickle cell disease.

Sickle cell disease

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

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

Most people with sickle cell trait have no medical issues as a result. The trait cannot develop into the disease.

Symptoms are rare, but 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
  • doing 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 sickle cell trait usually appear normal. When there is oxidative stress, however, they take on a sickle-like shape.

Most people with the trait experience no complications, though these can develop under extreme circumstances.

However, people with sickle cell trait may be more likely than other people to experience the following health issues:

  • muscle breakdown, called rhabdomyolysis, during exercise or training, especially in high or low temperatures
  • heatstroke
  • low blood supply to the spleen, leading to tissue death
  • glaucoma, following an eye injury
  • kidney disease
  • renal medullary carcinoma, a rare form of kidney cancer

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

While most experts consider sickle cell disease to be benign, there is some debate about the real rates of various complications.

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

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

The lack of funding for sickle cell trait and sickle cell disease stems from inequity in healthcare, and it is a problem that must be urgently addressed.

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

For this reason, it is crucial to understand how the trait is passed on and how likely it is to be inherited.

If both parents have sickle cell trait, there is:

  • a 50% chance that 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

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

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

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

Screening for sickle cell trait is now routine for newborns in the U.S.

For older children and adults, a doctor can diagnose sickle cell trait with a simple 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 sickle cell trait. Screening is also routine for athletes and people joining the military.

Sickle cell trait usually requires no treatment, as most people do not experience any symptoms.

However, it is a good idea to consult a doctor if a person knows that they have the trait and are planning to:

  • have children
  • be an athlete
  • join the military

Considerations during extreme exercise

People with sickle cell trait are more likely to have muscle breakdown or heat stroke when doing intense physical exercise, such as in 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 sickle cell trait, it is a good idea to speak with a genetic counselor before having children.

The counselor will look at the person’s family history and their partner’s, and discuss any relevant risks and considerations.

Sickle cell trait 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 — during extreme exercise, for example.

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

For this reason, it is a good idea for anyone with sickle cell trait to speak with a genetic counselor before having children.