Sickle Cell Trait

Medically Reviewed by Minesh Khatri, MD on August 14, 2022
6 min read

Sickle cell  trait (SCT) is a genetic blood disorder. That means it’s inherited or passed down from a parent to a child (or children). Sickle cell trait is different from sickle cell disease (SCD), and in fact isn’t considered to be a disease. People with SCD have “sickle” (crescent moon) shaped red blood cells due to an abnormal version of a protein called hemoglobin. They often have a lot of pain and other symptoms.

Having SCT means you inherited the sickle gene from one (not both) of your parents and most of your red blood cells are normal. It’s rare for people with SCT to have any symptoms. Most lead normal lives.


Sickle cell disease (SCD) is the result of a broken hemoglobin gene. Hemoglobin is the substance that carries oxygen inside red blood cells. You need two copies of this defective gene -- one from each parent -- to get sickle cell disease. (Doctors call this an autosomal recessive pattern of inheritance.) If both your parents have the problem gene, you have a 1-in-4 chance of being born with the disease.

People with SCT have one normal hemoglobin gene (“A”) and one abnormal hemoglobin gene (“S’). That’s why you sometimes see it called HbAS. If both your parents carry the sickle cell trait, you have a 50% chance that only one of them will pass it on to you. If they do, you’ll have SCT.

People who carry the sickle cell trait aren’t likely to get sick with SCD symptoms. 

Sickle cell disease is marked by abnormally shaped red blood cells (RBCs) that can lead to severe, painful attacks. Doctors call these attacks “crises.” Healthy red blood cells are round or disc-shaped and move easily through your small blood vessels. Sickle-shaped cells are hard and not as flexible as normal RBCs. They can get stuck in small blood vessels and cause clogs, pain and other problems like infections and stroke. They can also lead to a potentially deadly complication known as acute chest syndrome, which makes it hard to breathe. People with SCT have mostly normal red blood cells, so they don’t usually get these severe problems. 

Sometimes people with sickle cell trait do have symptoms, but it's rare. They could include:

  • Blood in your pee (Although this by itself isn’t always a problem, it’s a good idea to see a doctor to make sure nothing more serious, like a kidney problem, is going on.)

  • Pain at high altitudes

  • Difficulty exercising in extreme weather

Some people with sickle cell trait may be more likely than others to have heat stroke or dangerous muscle breakdown after intense exercise. This is especially true in extreme weather conditions of heat or cold. Athletes and military trainees with SCT are most likely to have these health issues. 

If you have SCT and are doing intense workouts, take these steps to avoid any problems:

  • Stay hydrated. Drink water before, during and after heavy activity.

  • Keep your body cool. Prevent overheating when it’s hot and humid by misting or taking breaks in air-conditioned areas.

  • Pace yourself during workouts. Start slowly and then build intensity.

  • Take frequent breaks or rest periods during training.

  • Seek medical help right away if you start to feel ill.

More than 100 million people across the world have SCT. About 1 in 12 African Americans and 1 in 100 Hispanic Americans are born with the condition. It’s also common in people whose ancestors are from:

  • The Mediterranean: Countries such as Turkey, Greece, and Italy

  • The Middle East: Countries like Saudi Arabia.

  • Asia: Countries such as India and Japan

  • Central and South America: Countries like Brazil and Costa Rica

Sickle cell trait (SCT) is passed down through families. If your parents have the trait, you may get sick from the disease (SCD), or you may only “carry” the gene (SCT) and never have symptoms. Learning how the trait is passed on can help you better understand what to expect.

If you have SCT, there’s a chance you could give the defective gene to your children. SCT isn’t a serious condition, but SCD is. It’s important to know if you and your partner both have sickle cell trait. If you do, there’s a 25% chance with each pregnancy of having a child with SCD. There’s also a 25% chance of having a child with no trait or disease (normal genes) and a 50% chance of having a child with sickle cell trait.

Your doctor can order a blood test to see if you carry the sickle cell trait.

Prenatal testing can tell if your baby has sickle cell disease or carries the sickle cell gene. Newborn screening programs require that every state in the U.S. test babies for SCD or the trait shortly after birth.

If you know or think you could have sickle cell trait and want to start a family, it’s a good idea to talk to a genetic counselor. These professionals have experience with genetic blood disorders and specialize in prenatal genetic counseling. They can help you figure out if SCD and SCT run in your family and if there’s a risk of giving abnormal genes to your child. Both you and your partner should be tested for SCT if you’re planning to have a baby.

There’s no specific treatment for sickle cell trait since most times there are no symptoms. Treatment would be focused on the rare symptoms or complications in a person with SCT.


Prevention of sickle cell trait centers around people with sickle cell disease or sickle cell trait making an informed decision with their partner and the help of a genetic counselor when planning a family. 

People with SCT can avoid getting rare symptoms and problems by being aware of dangerous situations, and taking precautions when considering exercising, hiking, flying, scuba diving and taking part in other extreme activities.

Sickle cell trait isn’t a mild form of sickle cell disease and can never become sickle cell disease. But the trait can make you more likely to get a certain type of kidney cancer and kidney disease, or have blood in your pee (hematuria). It may also raise your risk of blood clots. Athletes and those in extreme military training should take extra care, like drinking extra fluids and taking frequent breaks.

In rare and extreme cases, people with sickle cell trait can experience complications such as:

  • Pain crises similar to people with SCD

  • Splenic Infarction (tissue death) due to a lack of oxygen to your spleen. This can result from heavy exercise at altitudes above 5,000 feet. Symptoms include nausea, vomiting, and pain in your chest and abdomen. Get medical help right away if you have these problems.

  • Sudden death. People with sickle cell trait should be careful in situations of increased atmospheric pressure (like scuba diving), low oxygen, high altitude, and dehydration.

You can also pass the trait on to your children.