WASHINGTON — Thousands of families carry the gene that causes sickle cell disease and don't know it — even though almost every newborn today is tested for what's called "sickle cell trait," and starting this summer more college athletes are getting tested, too.

Spurred in part by rare but tragic collapses of athletes from overexertion, work is beginning to find families missed by newborn screening or who didn't understand that sickle cell trait has ramifications: Aside from sports safety, if both parents carry the gene they could have a baby with full-fledged sickle cell disease, a devastating blood disorder.

In late June, the NCAA recommended that colleges and universities test student-athletes, many of whom were born before widespread newborn screening. The move helped settle a lawsuit from the family of a 19-year-old freshman football player at Rice University, Dale Lloyd II, who died from sickle cell trait complications during a conditioning workout in September 2006.

"Athletes should be tested but so should everybody else," says Dr. Lakshmanan Krishnamurti of the Children's Hospital of Pittsburgh, whose sickle cell program, prompted by the NCAA recommendation, is preparing to offer testing for anyone in that city's schools, both high school and college.

"There is a lack of awareness all around," adds Krishnamurti, who spearheaded a separate effort to improve notification of new parents. "It's really quite a travesty."

Don't misunderstand: Sickle cell disease demands immediate treatment for babies, and state testing programmes make tracking down those families a priority. About 80,000 Americans have sickle cell disease, in which oxygen-carrying hemoglobin clumps inside red blood cells, turning them into a sickle shape that can't squeeze through tiny blood vessels. That causes pain, infections and eventually life-threatening organ damage.

Sickle cell trait is different. More than 2.5 million Americans have it, meaning they carry one copy of the abnormal hemoglobin gene, not the two needed to cause full disease. Trait carriers only occasionally experience health problems, like blood in the urine, some blood clumping at high altitudes and the athletes' risk — in which intense exercise can cause blood cells to sickle enough to block blood flow to muscles, which rapidly break down. The National Athletic Trainers Association, which also recommends athlete testing, has counted a dozen sports-related deaths since 2000 from that "exertional sickling," most of them college football players during training but also two 12-year-olds.

Testing is only half the story, cautions NATA's Scott Anderson, head athletic trainer at the University of Oklahoma. You can be a star athlete with sickle cell trait, but you and your coaches must be alert to symptoms, like cramps, and get quick treatment.

"If education and precautions don't follow the information that comes with screening, then the screening has really been done all for nothing," he says.

Sickle cell is most common in black Americans — about 10 percent have the trait — and also in people of Mediterranean, Middle Eastern and Central and South American ancestry. In short, almost anyone can have it.

Hence newborn screening, which many states offered in 1998 and which covered all newborns by 2006. But it was established to find disease, not generally healthy gene carriers, and specialists say there's wide variation in how aggressively the state programmes notify parents about sickle trait.

"We were caught off guard," says Andrea Williams of Pittsburgh, whose fourth child, Jonathan, was born with sickle cell disease in 2000. Because her mother-in-law insisted her husband wasn't affected, "I told the nurse that was not genetically possible."

But more testing confirmed it: Both Williams and her husband silently carried the sickle gene, and their two oldest daughters do, too. Although Pennsylvania was screening newborns before her second daughter's birth, no one contacted the family then so they could learn they were at risk.

Krishnamurti's programme has since improved newborn notification so that most affected families in western Pennsylvania get telephone genetic counseling, and 20 percent seek testing of family members, up from two percent in 2002. And Williams started the Children's Sickle Cell Foundation to, among other things, educate teenagers about sickle trait and get them tested before they start having children.

Perhaps trickier is whether parents know when to share the information. Oklahoma, a leader in college-athlete testing, has detected sickle trait in 19 football players in about a decade, and only two already knew it, Anderson says. Yet when the others called home with the news, only one had a parent who hadn't known.

"This is not totally benign, and they need to remember that," says Michele Lloyd-Puryear of the US Health Resources and Services Administration, which provides money to 17 communities to improve communication about sickle cell trait.

Last year the agency published new booklets that explain the genetics — for both new parents, and for teens or adults just now getting tested — in simple terms: If both mom and dad carry the abnormal gene, each pregnancy has a one in four chance of a child with full-blown sickle cell disease.