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Sickle Cell Trait

What is Sickle Cell Trait?

A hidden danger could be lurking for athletes who don't know their genes. During intensive exertion, athletes with the gene for sickle cell trait (SCT) are at risk for what is called exertional sickling. When this occurs, red blood cells change from their normal round shape to crescent shaped, causing a log jam in the blood vessels. Blood flow can then be disrupted.

Over the past three decades, at least 15 athletes, including two in 2010, collapsed after intense exercise and died due to complications from SCT, according to the National Athletic Trainers' Association.

"You can't minimize this condition," said Jim Muntz, M.D., co-medical director of the IRONMAN Sports Medicine Institute at Memorial Hermann and team doctor for the Astros, Rockets and Texans. "Someone with the trait could get into trouble within three minutes of starting to exercise."

Having treated professional athletes since the days of the Houston Oilers, Dr. Muntz is passionate about educating the athletic community about SCT. He's also quick to say that with proper precautions, SCT isn't a barrier to safe athletic participation. Dr. Muntz points to NBA and NFL players with the trait who perform at exceptional levels of stress and competition.

Testing for SCT

Individuals with SCT inherit one gene for sickle hemoglobin and one for normal hemoglobin. This is different than sickle cell disease in which an individual inherits two sickle genes.

One in 12 African Americans in the United States carries SCT. The gene is rare, but not unheard of in Caucasians. University of Georgia Head Coach Mark Richt, who is Caucasian, has a son who tested positive for sickle cell. SCT is also present in those of Mediterranean, Middle Eastern, Caribbean, South American and Central American descent.

Organizations such as the March of Dimes and the American College of Medical Genetics recommend testing newborns for hemoglobin disorders such as sickle cell. Texas is one state that follows these guidelines, but newborn screenings differ from state to state. Therefore, athletes are encouraged to contact the doctor where they were born to see if the screening was performed, or to discuss the testing with their family physician or pediatrician.

There is no required SCT testing for high school athletes, but the UIL pre-participation health physical questionnaire asks about it in the history section. The NCAA now requires all Division I athletes to undergo testing for SCT. The change was championed by Rice University after a 19-year-old freshman died in 2006 following an intense football workout. It was later learned the athlete had SCT.

Know When to Modify Workouts

Testing is only the first step. It's also important to know the symptoms - and when to modify workouts and get quick treatment.

Symptoms of exertional sickling include muscle cramping, bone pain, swelling, weakness, fatigue and difficulty breathing. These can arise when there is intense physical exertion with little recovery time, such as repeated wind sprints. Particularly problematic are conditions that combine intense physical exertion with situations that stress the body, such as severe heat, dehydration, asthma, high altitudes and racing to high intensity without adequate pace progression.

Since the symptoms of exertional sickling and heat exhaustion are similar, Dr. Muntz helps clarify the difference. "If an athlete is sickling, his or her muscles may be limp and flabby, not tight like you'd see with heat cramps," he said, noting that sicklers collapse whereas other athletes hobble off the field. "This might change how you care for the athlete. If the muscles are flaccid rather than stiff, the athlete might require oxygen in addition to intravenous fluid."

In 2007, the National Athletic Trainers' Association (NATA) issued a consensus statement calling for athletes with SCT to be pulled from training if they exhibit any of these symptoms. They also shared research findings that targeted end-of-practice sprints as particularly dangerous. As a result, NATA recommended athletes with SCT be excluded from performance tests like stadium step runs, uphill runs, serial sprints and mile runs.

Ultimately, it is vital that coaches and athletic trainers know which athletes have SCT and closely monitor their workouts to prevent emergency situations. Athletic trainers with the IRONMAN Sports Medicine Institute at Memorial Hermann are well educated about SCT and find it prominently discussed in continuing education programs.

For athletes with SCT, year-round strength and conditioning programs are necessary. So is pace progression and the addition of longer periods for rest and recovery. Athletes must be keenly aware of the symptoms of sickling and stop all activity should any of them occur. Finally, athletes with SCT should not fear reprisal from coaches if they ask for modifications to their workout during extreme heat conditions.