Sickle cell trait means you carry one copy of the sickle cell gene and one copy of the normal hemoglobin gene. It is not sickle cell disease, and it does not turn into sickle cell disease over time. About 1 in 13 Black or African American babies in the United States is born with sickle cell trait, and the vast majority of carriers live normal, full lives without symptoms.
How Sickle Cell Trait Differs From Sickle Cell Disease
The distinction comes down to one gene versus two. People with sickle cell trait inherited a sickle hemoglobin gene (called HbS) from one parent and a normal hemoglobin gene (HbA) from the other. Because their body still produces plenty of normal hemoglobin, their red blood cells function well under everyday conditions. People with sickle cell disease, by contrast, inherited two copies of abnormal hemoglobin genes and cannot produce normal hemoglobin A at all. Their red blood cells break down quickly and deform into the crescent or “sickle” shapes that give the disease its name, causing chronic anemia and painful episodes.
Sickle cell trait does not shorten your lifespan. A study tracking nearly 50,000 active-duty U.S. Army soldiers found no increase in mortality among those who carried the trait, provided they followed standard precautions against dehydration and overheating. Most carriers never experience serious medical problems related to their status.
How You Find Out
In the United States, every state screens newborns for sickle cell disease and trait using a small blood sample, typically from a heel prick. The lab separates different types of hemoglobin to identify which variants are present. Results are usually available before a baby is two months old, well before symptoms of sickle cell disease would appear. If a screening result suggests sickle cell trait, a follow-up blood test with a complete blood count and a second hemoglobin analysis confirms the finding. Premature babies born before 33 weeks of gestation generally need repeat testing.
Adults who were never screened or don’t know their results can get a simple blood test called a hemoglobin electrophoresis through their doctor.
When the Trait Can Cause Problems
While sickle cell trait is overwhelmingly benign, it isn’t entirely without risk. Problems are most likely when your body is under unusual physical stress and needs more oxygen than normal. Situations that raise the risk include intense physical exertion, high altitude (mountain hiking or unpressurized aircraft), dehydration, and extreme temperatures.
Under those conditions, the small proportion of sickle hemoglobin in your blood can cause some red blood cells to sickle, potentially leading to muscle breakdown or, very rarely, sudden collapse during intense exercise. The military addressed this directly: after implementing enforced hydration protocols and closer monitoring of environmental conditions, sudden unexpected deaths dropped across 2.3 million recruits, with none occurring among the 40,000 who carried sickle cell trait.
The NCAA has adopted similar guidelines for college athletes. Their recommendations are straightforward: set your own pace during conditioning, build up gradually in preseason, take adequate rest between repetitions, stay well hydrated in hot or humid conditions, skip activity when you’re sick, and stop immediately if you experience unusual muscle pain, weakness, or breathlessness. Supplemental oxygen should be available at high altitudes.
Kidney Health Deserves Attention
The one area where sickle cell trait carries a more meaningful long-term risk is kidney health. The inner part of the kidney, called the medulla, is naturally low in oxygen and high in salt concentration. That environment can trigger sickling even in carriers, which over time may damage the small blood vessels there.
A large analysis of nearly 16,000 African Americans found that participants with sickle cell trait had a higher risk of developing chronic kidney disease and experienced a faster decline in kidney function compared to those without the trait. A separate study of about 10,000 African Americans confirmed that carriers faced nearly twice the risk of kidney failure. Some carriers also experience blood in the urine, which results from damage to the kidney’s inner tissue. While this is often harmless, persistent or recurring blood in the urine should be evaluated because, in rare cases, it can signal a kidney cancer called renal medullary carcinoma. This cancer is uncommon but aggressive: in a review of 217 cases, 88% occurred in people with sickle cell trait.
None of this means kidney disease is inevitable for carriers. It does mean that keeping an eye on kidney function through routine checkups is worthwhile, especially if you have other risk factors like high blood pressure or diabetes.
Why the Trait Persists: Malaria Protection
Sickle cell trait is most common in people whose ancestors came from regions where malaria was historically widespread, including sub-Saharan Africa, the Mediterranean, the Middle East, and parts of India. That’s not a coincidence. Carrying one copy of the sickle gene offers significant protection against the deadliest form of malaria.
The protection works on multiple levels. The malaria parasite has a harder time invading and multiplying inside red blood cells that contain some sickle hemoglobin. Infected cells also tend to sickle, which flags them for destruction by the spleen before the parasite can mature. On top of that, research in Gambia and Sudan found that carriers develop stronger immune responses to malaria, recognizing and attacking infected cells more effectively. This combination of physical and immune defenses gave carriers a survival advantage in malaria-endemic regions, which is why the gene remained so common across generations.
What It Means for Having Children
Sickle cell trait matters most in family planning when both partners carry it. If both parents have the trait, each pregnancy carries a 25% chance the child will have sickle cell disease, a 50% chance the child will have sickle cell trait, and a 25% chance the child will have neither. If only one parent carries the trait, none of their children will have sickle cell disease, though about half may inherit the trait.
It’s also possible to have sickle cell disease by inheriting one sickle gene and one copy of a different abnormal hemoglobin gene, such as hemoglobin C. This is why genetic counselors sometimes recommend that both partners get hemoglobin testing before or during pregnancy, even if only one is known to carry a hemoglobin variant.