The Mile High City always seemed to cause Clark big problems.
An eerily similar pain crept up shortly after the Steelers' 31-28 loss on Oct. 21, 2007.
This wasn't a bruise or a contusion and the pain didn't dissipate over time with medication as it had before. Clark was experiencing a serious reaction to a blood condition known as sickle cell trait, which can cause a carrier's normally round red blood cells to collapse when a person is under extreme physical duress. The blood gets sticky and can clog arteries, preventing oxygen from being carried to vital organs.
Clark's symptoms lingered for days as perplexed doctors tried to understand why his body continued to shut down.
"I remember having a doctor tell me 'I'm gonna pray about it' and I was like 'You're supposed to believe in medicine. I got my Bible, I'm gonna pray, you go read a book and try to figure this out,'" Clark said.
Doctors ultimately removed his spleen and gallbladder and Clark soon learned that great exertion in high altitude caused his sickling episodes. It was all news to him. Clark was told he had sickle cell trait shortly after joining the NFL, but he had no idea what the condition meant or that it could kill him under the certain circumstances. Since 2000, 17 athletes' deaths have been tied to complications from sickle cell trait. That includes nine college football players — by far the biggest killer in that sport during the time period.
"In the league you take different types of blood tests and they came to me and said you have the sickle cell trait," Clark said. "And immediately following that statement was 'but it's no big deal.'"
Clark's situation is not unusual. Even though every baby in the United States is tested for sickle cell trait at birth, many athletes who've had it either didn't know or didn't understand what it meant.
Former Auburn receiver Tyron Goodson didn't know about the trait's potential impact when he collapsed after a training run in the mid-1990s. Former Florida State receiver Devard Darling knew his sickle cell status, but he was unaware of the life-threatening risks. Darling's twin brother, Devaughn, died from complications of the trait during offseason football conditioning in 2001.
Brandon Antwine played his entire high school career not knowing he had the trait, learning it from the University of Florida football staff. That knowledge helped athletic trainers save his life during a sickling episode he suffered during practice in 2007.
Head athletic trainer Scott Anderson said the University of Oklahoma had 20 athletes who tested positive for sickle cell trait during the 2009-10 school year. Just three knew they had it before being told by the school, and none had a clear grasp of the precautions Anderson believes should be taken before playing sports.
"Unfortunately, there are too many athletes who don't know their status, don't know how to answer it," Anderson said. "They assume the answer is no, they don't have the trait."
Currently, the NFL tests new players for sickle cell trait at its combine every season. In March 2010, the Florida High School Athletic Association revised its annual physical form to add questions about the trait. This summer, the National Federation of High School Associations sent its 2011 sports medicine book to every high school in the country with a chapter on educating athletic trainers about sickle cell trait.
And last April, the NCAA approved a new rule stating all Division I athletes must either be screened for sickle cell trait or sign a liability waiver indicating they do not want to be tested. The rules were established, in part, because most players don't realize they've been tested before.
For starters, different states have different procedures for informing parents about their babies' sickle cell trait. Some receive a letter and are directed to hospitals for confirmation tests and counseling. Some only receive a phone call. Parents don't receive the actual test results. Instead, the information is passed directly to the child's primary physician.
"Although the information is there, many families don't recall having received the information," said Dr. Lanetta Jordan, director of Sickle Cell Services at Memorial Healthcare System in South Broward. "I think they are at least notified, but people move, people forget information. If your baby isn't sick, then it's something that's not really maintained and there's no follow-up component."
Jordan recommends widespread public education about sickle cell trait so families know their baby has been tested and how and where to access the information.