01/05/2012 03:50 pm ET Updated Jan 05, 2012

Pittsburgh Steelers' Ryan Clark Benched For Sickle Cell Trait. What Triggers It?

The last time Pittsburgh Steelers' Ryan Clark played a game in Colorado, he nearly died, the Associated Press reports, highlighting a series of health scares that led to this week's decision by coach Mike Tomlin to bench the 32-year-old safety during this Sunday's wildcard game in Denver.

"They couldn't tell me 100 percent that 'Nothing is going to happen to you, you're going to play and you're going to be fine' and I think that one percent chance was enough for coach Tomlin to take it out of my hands," Clark told the AP, referring to his battle with sickle cell trait (SCT), which occurs when a person carries a single copy of the sickle globin gene inherited from one parent along with a normal globin gene from the other parent. (Sickle cell trait is different from sickle cell disease, also known as sickle cell anemia.)

According to the CDC, certain conditions can cause flare-ups in people with SCT, including dehydration, low oxygen levels in the air and high altitudes like the one Clark experienced in Denver, causing a "crisis" that eventually forced him to have his gall bladder and spleen removed in addition to losing 30 pounds.

Tomlin reportedly told Clark that if his own son Dino was in the same situation, he wouldn't let him play, a decision he delivered to Clark just one day after former University of Tulsa football player George Clinckscale's death was determined to be the result of sickle cell trait complications.

While many people with SCT don't experience symptoms at all, athletes' intense exercise regimens tend to act as triggers among those who carry the trait, prompting officials, like Tomlin, to take more stringent measures to keep players safe.

On the college level, the NCAA has implemented mandatory SCT screening of all Division I student-athletes. The impact of their initiative was evaluated last month by researchers at the University of Michigan who found that testing alone will help identify more than 2,000 athletes with SCT, but they warned that screening alone will not prevent death.

"In addition to educating athletes and staff, precautionary measures need to be strictly enforced," said Beth A. Tarini, M.D., M.S., lead author of the study and assistant professor in the Department of Pediatrics and Communicable Diseases at the University of Michigan.

The CDC makes the following recommendations for people with SCT who play competitive or team sports:

  • Set your own pace and build your intensity slowly.
  • Rest often in between repetitive sets and drills.
  • Drink plenty of water before, during and after training and conditioning activities.
  • Keep the body temperature cool when exercising in hot and humid temperatures by misting the body with water or going to an air conditioned area during breaks or rest periods.
  • Immediately seek medical care when feeling ill.

SCT is most common among Blacks or African Americans, affecting 1 in 12 Blacks or African Americans in the United States. It can be found, however, among people whose ancestors come from sub-Saharan Africa; the Western Hemisphere (South America, the Caribbean, and Central America); Saudi Arabia; India; and Mediterranean countries such as Turkey, Greece, and Italy, according to the CDC.