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Gender matters in plasma transfusions
2007-01-22
The plasma transfused into victims of burns, car crashes and other serious conditions soon will come almost completely from men. Make no mistake: Women need to donate blood now more than ever as blood supplies become more precarious each year. But blood banks are beginning to separate out women's plasma -- the liquid part of blood -- in an effort to fight a mysterious lung injury that has become the nation's leading risk from transfusions. Ask about blood safety and most people think of HIV or other diseases that, thanks to strict testing, actually are incredibly rare in U.S. transfusions. Today the top threat is TRALI, or "transfusion-related acute lung injury," in which transfusions trigger reactions that fill patients' lungs with fluid, leaving them gasping for air. There are no good counts, although TRALI is thought to strike a few hundred people a year and kill roughly 10 percent of them. It's a condition doctors don't always recognize since patients who need transfusions are seriously sick to begin with, but it's starting to gain attention. "This is a bigger problem than we were aware of," says Dr. Richard Benjamin, chief medical officer of the American Red Cross. He began studying TRALI when cases reported to his agency almost doubled in two years. No one knows exactly what causes TRALI. But certain immune cells carried by women who have been pregnant are emerging as a chief culprit, cells called antibodies that mothers-to-be produce in reaction to their fetus' foreign father cells. The antibodies do no harm to mother, baby or the vast majority of people who encounter them in a transfusion. To get TRALI requires what Celso Bianco of America's Blood Centers calls "a horrible coincidence" in which the transfusion recipient has white blood cells that just happen to recognize and clash with the donor's antibodies. When blood is donated, it is separated into its major parts -- oxygen-carrying red blood cells that make up most transfusions, plus platelets and plasma. Those problem antibodies seem to cluster most in plasma. Indeed, Benjamin found 60 percent of TRALI fatalities reported to the Red Cross were linked to plasma transfusions. That's good news, because it points to an easy way to reduce TRALI. Only about a quarter of the plasma that blood banks collect is directly transfused. The rest is used to manufacture other lifesaving blood products, such as clotting factors for hemophiliacs or infection-fighting immune globulin. So three years ago, Britain began an experiment: reserving male-donated plasma for transfusions, and separating plasma donated by women for manufacture into those other drugs. TRALI cases plummeted, researchers reported at an international blood meeting last fall. Now U.S. blood banks are following suit. The Red Cross, which provides about half of the nation's blood supply, already has shifted to about 95 percent male-donated plasma for transfusions in a few parts of the country and is expanding the policy nationwide this year. A number of independent blood banks, which provide the other half of the nation's blood, are making the switch, too. Altogether, the change could prevent about 150 cases of TRALI a year, and 15 deaths, estimates Dr. Patricia Kopko, medical director of BloodSource, a California blood bank that made the male-donor shift on Jan. 1. The switch won't mean all female-donor plasma goes to drug-making; supply problems mean a little still will be needed for direct transfusions. Nor does it completely solve TRALI. "We're fixing the biggest problem first," says Benjamin. Here's the puzzle: If these common antibodies were TRALI's only trigger, the lung ailment would be common, too. Instead it's rare, occurring about once per 5,000 units of transfused blood products. Something has to "prime" the lungs to be susceptible, explains Dr. Christopher Silliman, a pediatric hematologist at the University of Colorado and Denver's Bonfils Blood Center. The patient's initial disease, or some other factor such as undergoing anesthesia, appears to make the lung's lining hyperactive. Only then can antibodies -- or other substances that break down in blood products as they age -- infiltrate the lung and hurt it. Also, the implicated antibodies aren't just in plasma. Smaller concentrations are in blood-clotting platelets, which are in such short supply that blood banks could never use only those from men. Blood banks are hunting other solutions, such as ways to test which donors have high antibody levels. Only because blood is so protected today from infections can scientists tackle TRALI -- and they worry that the gender focus might deter women from giving blood at a time when every donor is critical. Demand for blood is rising annually, yet only 5 percent of Americans eligible to donate do so and each year brings periodic shortages. Women should "not get the idea that they are not needed, because they are vitally needed," Kopko stresses. "We transfuse a whole lot more red blood cells than plasma." ___ EDITOR'S NOTE -- Lauran Neergaard covers health and medical issues for The Associated Press.
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