Sickle cell trait (SCT) is an inherited condition that can be tricky to understand. It is not the same as
sickle cell disease (SCD), red blood cell disorders that affect hemoglobin, the protein that carries oxygen through the body. In fact, SCT is not a disease at all. Rather, people with sickle cell trait are born with and carry
one gene for sickle cell hemoglobin and one for regular hemoglobin.
Read on to learn what this means for a child with the condition, and questions families may have about sickle cell trait.
How common is sickle cell trait?
Sickle cell trait is more common in people whose ancestors are from Africa or the Middle East. It is also frequently seen in descendants of people from the Mediterranean (Italy, Turkey, Greece, India), the Caribbean and Atlantic Coast of central and South America. Anyone can have SCT. There are 3-4 million people in the U.S. who have it, and 300 million worldwide. About 1 in 12 African Americans and 1 in 150-200 Caucasians have SCT.
Can sickle cell trait turn into sickle cell disease?
Sickle cell trait only rarely may put a person at risk for medical problems. Sickle cell trait does not go away, nor will it develop into sickle cell disease. Once a person is diagnosed with SCT, they do not need another test. But while someone with SCT won't develop SCD, they can pass it on genetically to their children.
How is sickle cell trait inherited?
We all have two copies of nearly every gene in the body, including two copies of the gene that makes hemoglobin. One copy of the hemoglobin gene comes from each parent. The normal gene for hemoglobin is called "A." The sickle cell hemoglobin gene is called "S."
People with sickle cell trait inherit one normal hemoglobin gene "A" from one parent and one sickle hemoglobin gene "S" from another parent. People who have sickle cell DISEASE inherit two abnormal hemoglobin "S" genes. There are also other unusual hemoglobins that may interact with "S" to cause sickle cell disease, including hemoglobin C trait, beta thalassemia trait, and hemoglobin D Punjab and other disorders.
How likely is a child to inherit sickle cell trait from a parent who has it?
People with sickle cell trait have a 50:50 chance for each child to inherit it. If two people with SCT have a baby, there is a 50% chance of inheriting SCT from each parent; so, there is a 25% chance of each child having normal hemoglobin, a 50% chance of having SCT, and a 25% chance of having SCD. That is, if two people with SCT have a baby 1 in 4 of those pregnancies will result in a baby with SCD and 2 in 4 in a baby with SCT. So, if you have SCT, be sure that your partner knows if they also have SCT or a different abnormal hemoglobin trait to understand your risk of having a child with SCD.
How does sickle cell disease affect people?
Sickle cell disease occurs when people are born with
two abnormal hemoglobin genes, either two sickle cell hemoglobin genes, or one sickle cell gene and one other abnormal hemoglobin gene. When this happens, a person can only make the abnormal hemoglobin. In sickle cell disease, the abnormal hemoglobin causes the red blood cells to turn into a banana or "sickle" shape that get stuck in small blood vessels. Clogged blood vessels may prevent oxygen from being delivered to some parts of the body, causing pain and other serious problems. Sickle cell disease can be a very serious disease, but remember that people with SCT do NOT have sickle cell pain or these problems.
What is sickle cell anemia?
Sickle cell anemia (SCA) is the name of the most common type of sickle cell disease. It usually refers to the type of sickle cell disease in which the person has two hemoglobin S or sickle cell genes. People with SCT will not turn into someone with SCD or SCA, however SCT carriers are at risk for passing the trait onto their children or depending on the trait status of their partner of having a child with SCD or SCA.
It is important to remember that if a child has sickle cell trait, at least one of their parents also has it. Siblings may also have sickle cell trait. If you do not know your sickle cell trait status, talk with your doctor to get tested.
What are some of the rare health issues related to sickle cell trait?
Heat and exercise-related illness: After intense physical activity, anyone can be at risk for heat stroke (exertional rhabdomyolysis). Warning signs of heat stroke include generalized weakness, difficulty breathing, dizziness or excessive sweating. While people with sickle cell trait are at increased risk for serious complications from heat related illness, very few people with SCT actually experience it.
To prevent heat stroke drink plenty of
water before, during and after exercise. It is also a good idea to rest between exercise periods, take time to slowly adjust to high altitude, humidity, and/or heat. (See more information about playing sports below.)
Blood in the urine (hematuria): This may be due to a structural problem in the kidney, inflammation, an infection, or rarely a tumor called a renal medullary carcinoma. If you have sickle cell trait and blood in the urine, please tell your doctor so a complete evaluation can be done.
Chronic kidney disease is slightly more common in some people with sickle cell trait as they get older. While there is no known way to avoid kidney failure, ways to help slow the disease are to eat a healthy diet, control blood pressure and
exercise regularly throughout life to decrease the risk of
Loss of vision after an eye injury: If there is bleeding in the eye after an injury (called a traumatic hyphema), people with sickle cell trait may develop high pressure in the eye called
glaucoma. Glaucoma may cause temporary or permanent blindness. If you have an eye injury and SCT, be sure to see a doctor tell them you have sickle cell trait.
Splenic infarct: This condition affects the spleen, an organ in the left upper side of the abdomen that helps fight infection. Very rarely when oxygen levels are low, the blood flow may be blocked to all or part of the spleen, causing pain, trouble breathing and nausea. This is more common with going quickly to very high altitudes (like high mountains), flying in unpressurized (not modern commercial) aircraft, scuba diving, during intense exercise and with dehydration. If you have sickle cell trait and develop unusually severe pain on your left side, please contact your doctor right away.
Blood clots: There is a small increased risk of blood clots in the lungs (pulmonary embolism) and perhaps other places in the body. At baseline
d-dimer, a test used to diagnose blood clots and monitor anti-coagulation, are elevated with sickle cell trait. If you are being evaluated for a blood clot be sure to tell your doctor that you have SCT.
Inaccurate diabetes blood test: The blood test most commonly used to screen and follow pre-diabetes,
Hemoglobin A1C, may not be an accurate way to measure blood sugar control in people with sickle cell trait. Again, if you have SCT tell your doctor so they can ensure the hemoglobin A1C test is done by a technique that avoids this problem.
Can my child with sickle cell trait play sports?
Yes! Exercise and regular physical activity are healthy for everyone, including people with sickle cell trait. Everyone, with and without SCT, should take precautions to prevent exercise-related illness such as heat stroke, severe dehydration, and muscle tissue breakdown (rhabdomyolysis). These conditions are rare but may become severe. Studies have shown that when precautions to minimize the risk of exercise-related illness are used, athletes with SCT can safely participate in intense sports training.
Tips to prevent exercise-related illness with sickle cell trait:
- Work on conditioning slowly. Begin exercising with low intensity, especially at tryouts or the beginning of the sports season. Gradually increase exercise frequency and intensity (repetitions) as tolerated. Have an exercise or conditioning plan to get in shape slowly.
- Decrease exercise intensity during times of high heat, humidity, and altitude.
- Stay well hydrated by drinking plenty of water before, during, and after exercising.
- Do not drink alcohol, caffeine, or energy drinks around the time of exercising. These actually cause dehydration.
- Limit exercise when sick. If sick during exercise, stop and seek medical help.
- Take breaks from exercising and be sure you or your child knows to report to the coach or trainer any of these symptoms:
- muscle weakness
- cramps or pain
- a feeling that heaviness in the legs
- rapid breathing
- lightheadedness or dizziness
- feeling overheated
Testing student athletes for sickle cell trait
Some high school and college athletic associations recommend that participants be tested for sickle cell trait so that coaches can be aware and prevent exercise-related illness. However, if you know you have SCT and can provide the test results, the test does not need to be repeated.
Is pregnancy risky if I have sickle cell trait?
Women with sickle cell trait should have no medical problems during pregnancy or delivery of their children. However, some women with SCT may be at increased risk of blood clots during pregnancy. Be sure to talk with your obstetrician if you have SCT and become pregnant.