People who carry one copy of a genetic variant called hemoglobin S (HbS) have sickle cell trait. Usually, it does not cause symptoms. However, when a person inherits two copies of HbS — one from each parent — they have sickle cell anemia.

Unlike sickle cell trait, sickle cell anemia is a blood disorder that requires ongoing medical care. It occurs because red blood cells become sickle-shaped, or C-shaped, instead of round. This interferes with the blood cells’ ability to transport oxygen around the body.

In contrast, sickle cell trait is benign. Having sickle cell trait simply means that a person carries a specific gene. However, it is important for people to know whether they have sickle cell trait, particularly if they want to have children.

Read on to learn more about the differences between sickle cell trait and sickle cell anemia.

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People with sickle cell trait carry a gene known as HbS. This gene affects how the body makes hemoglobin, the substance in red blood cells that transports oxygen around the body.

Usually, humans inherit two copies of a different gene, called hemoglobin A (HbA), from their parents. This gene tells the body to make healthy, round blood cells that carry oxygen effectively.

People with sickle cell trait inherit one copy of HbA and one copy of HbS. HbS tells the body to make hemoglobin in a way that makes red blood cells less effective.

Despite this, people with only one copy of HbS typically experience no symptoms. On its own, this gene affects only a fraction of the blood cells a person produces, meaning that only a few become sickle-shaped.

However, in situations that put immense stress on the body — such as intense exercise or low oxygen environments — people with sickle cell trait may develop more sickle-shaped red blood cells.

This can lead to symptoms similar to those of sickle cell disease or complications such as rhabdomyolysis. In severe cases, strenuous exercise may cause death.

Sickle cell anemia is a disease that a person gets when they inherit two copies of HbS — one from each parent.

Usually, red blood cells have an oval shape with a small dip in the middle. This shape allows them to move smoothly through veins and arteries and effectively deliver oxygen to cells.

However, in sickle cell anemia, the red blood cells become sickle-shaped. This causes them to get stuck in blood vessels and prevents them from delivering oxygen effectively. It also increases the risk of blood clots and damages the red blood cells, meaning they die earlier than they should.

Because every part of the body needs oxygen, sickle cell anemia has a widespread effect on health. The potential complications include:

  • infections
  • cardiovascular disease
  • chronic kidney failure
  • pulmonary hypertension
  • stroke
  • sickle cell crisis

Yes — a person who has sickle cell trait, by definition, does not have sickle cell anemia.

People with sickle cell trait carry only one copy of HbS, the gene that can affect hemoglobin production. The other gene, HbA, results in healthy red blood cells. This means the person does not have any form of sickle cell disease.

People with sickle cell trait usually have similar levels of health, quality of life, and mortality to people without the HbS gene.

Sickle cell trait usually causes no symptoms. Rarely, a person may experience symptoms similar to those of sickle cell disease during times of intense physical stress.

The symptoms of sickle cell disease include:

  • pain and swelling in the hands and feet
  • frequent infections
  • chronic pain
  • breathing difficulties, especially during times of stress

Symptoms typically start a few months after birth.

The process for diagnosing sickle cell trait and sickle cell anemia is often the same. Doctors use a blood test to check a person’s hemoglobin genes.

In the United States, this test is part of the newborn screening exam, which is a blood test doctors perform on babies during the first few days of life. Most people with sickle cell disease in the U.S. receive their diagnosis after this screening.

Sickle cell trait does not usually require medical intervention, but sickle cell anemia does. Treatment often focuses on two goals: maintaining health and managing complications.

Health maintenance involves regularly monitoring a person’s health. This may involve:

  • vaccinations to prevent infections
  • preventive antibiotics
  • health screenings to detect early signs of complications such as stroke
  • chronic transfusion therapy, which means a person receives regular blood transfusions

How doctors address complications will vary depending on the condition a person develops. It may involve:

  • pain medications
  • oxygen therapy
  • hydroxyurea for frequent or severe complications

One treatment, a type of bone marrow transplant, can cure sickle cell disease. However, not everyone is eligible because it involves undergoing chemotherapy, which is risky for people with sickle cell disease. It also requires a suitable donor.

Learn more about hematopoietic stem cell transplants.

The genes that cause sickle cell disease are more common in certain populations, including:

  • people of African descent
  • people of Middle Eastern, Mediterranean, or Asian descent
  • Hispanic people from Central and South America

In the U.S., sickle cell disease is most common in African Americans. About 1 in 12 African Americans have sickle cell trait, while around 1 in 500 African Americans have some form of sickle cell disease.

Some scientists believe that this could be an evolutionary response to malaria. Malaria is a parasitic infection that a specific species of mosquitos transmit when they bite humans. The parasite enters the blood and infects red blood cells.

When a person has one copy of HbS, their immune system eliminates any sickle-shaped blood cells, including any infected blood cells. This may reduce the severity of malaria symptoms.

Scientists speculate that sickle cell trait may be an adaptation that helps people survive in areas where malaria is a high risk.

People with sickle cell trait have a similar average life expectancy to the rest of the population. Sickle cell disease shortens a person’s life expectancy. People with sickle cell anemia need ongoing care and may have many symptoms.

Treatment options and approaches are improving, which means some people with sickle cell disease can live long lives. There are also promising gene therapies that may cure the disease.

However, this relies on people having access to high quality medical care.

Barriers to treatment

In the U.S., the people most likely to have sickle cell disease are also the most likely to have difficulty getting the care they need.

A 2020 article in the New England Journal of Medicine highlights how racism and socioeconomic inequity contribute to this, reinforcing barriers such as:

  • lack of funding
  • social stigma
  • difficulty getting pain medication
  • inconsistent or inadequate treatment

People who are having difficulty getting treatment may be able to get help from advocacy groups such as the Sickle Cell Disease Foundation. The foundation provides a “Find a Doctor” search tool, free counseling, and more.

Learn more about racism in healthcare.

A person has sickle cell trait if they carry one copy of the HbS gene. Sickle cell trait is typically a benign condition, but it does mean that a person’s child has a higher risk of sickle cell disease. It may also cause symptoms in certain situations and increase the risk of certain health complications.

Sickle cell disease is a serious illness that occurs when someone has two copies of HbS. People usually get a diagnosis at birth and develop symptoms as babies.

It is important for people with sickle cell trait to know they have it so that they can make informed family planning decisions and identify circumstances that might trigger symptoms.