What Is Sickle Cell Trait?

If it isn't a disease, why should you care about it?

Having sickle cell trait means you are a carrier for the sickle cell gene. The sickle cell gene is a small piece of DNA that passed down from parents, just like gender (male/female) or hair color, that causes someone to make sickle hemoglobin.

Woman holding a baby


Is Sickle Cell Trait a Disease?

No. At birth, you either have sickle cell disease or you don't. If you have sickle cell trait it cannot change into sickle cell disease.

Will Sickle Cell Trait Cause Me to Have Any Medical Problems?

It's not likely. In rare circumstances, sickle cell trait can cause sickling of the red blood cells, leading to complications. In general, this only occurs in extreme circumstances like dehydration, high altitudes, or low oxygen levels. Most people with sickle cell trait live their entire lives without any issues secondary to the sickle cell trait. It's important to remember this if you feel overwhelmed about having the trait.

In rare circumstances, a person with sickle cell trait may develop a rare kidney cancer called renal medullary carcinoma. The connection is not fully understood, but almost every person who has developed this cancer also has sickle cell trait (and occasionally sickle cell disease). Because of this connection, persistent side/back pain and/or blood in the urine (hematuria) in someone with sickle cell trait should be taken seriously.

Why Knowing Matters

Knowing whether you have sickle cell trait is most important when you are ready to have children. If you have sickle cell trait, you make hemoglobin A (normal adult hemoglobin) and hemoglobin S (sickle hemoglobin). This is sometimes abbreviated as AS. Fortunately, the body makes more hemoglobin A than hemoglobin S, which is why people with sickle cell trait rarely have problems.

The problem comes if your partner also has sickle cell trait. Sickle cell disease is inherited as an autosomal recessive condition. If both parents have sickle cell trait (AS + AS), there are three possibilities for their children: 25% chance of having a child with normal hemoglobin (AA), a 50% chance of having a child with sickle cell trait (AS), and a 25% chance of having a child with sickle cell disease. This chance of having a child with sickle cell disease occurs with each pregnancy, regardless of what happened in prior pregnancies.

It's not enough to know whether your partner has sickle cell trait or not because sickle cell trait can be in combination with other hemoglobin conditions like hemoglobin C trait and beta-thalassemia trait. If one parent has sickle cell trait (AS) and the other hemoglobin C trait (AC), there are four possibilities: AA (25%), AC (25 percent), AS (25%), and SC. Hemoglobin SC is a form of sickle cell disease. Similarly, sickle beta-thalassemia is a form of sickle cell disease.

How to Find Out

Currently, all children born in the United States are tested for sickle cell disease on the newborn screen. This allows children with sickle cell disease to start treatment before complications start. This test will also identify children born with sickle cell trait. If you were born before all children were tested or you simply don't know, you can ask your physician to test you for sickle cell trait.

There are two tests commonly used to determine sickle cell trait status. The first is the sickle solubility test, also known as a sickledex. The problem with the sickledex is that a positive result only tells you whether sickle hemoglobin is present or not. A positive result can occur in both sickle cell trait and sickle cell disease.

A more specific test is often called the hemoglobin electrophoresis or profile. This test identifies the different types of a hemoglobin a person has. In general, people who have sickle cell trait make about 60% hemoglobin A and 40% hemoglobin S.

Although having sickle cell trait should not cause you any problems, knowing your (and your partner's) sickle cell status will help you understand your risk of having a child with sickle cell disease in the future.

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