(Editor's Note: This story has been altered. P-I reporter Carol Smith contributed information from a Seattle blood center and emergency room to this story. The information was attributed incorrectly to another reporter in the original version of this story.)

WASHINGTON -- 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.

Currently about half the blood donations for Western Washington come from women, said a spokesman for the Puget Sound Blood Center. "If they couldn't donate, it would definitely have an impact."

In "transfusion-related acute lung injury," or TRALI, transfusions trigger reactions that fill patients' lungs with fluid, leaving them gasping for air.

TRALI is thought to strike a few hundred people a year and kill roughly 10 percent of them.

"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 nearly 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.

Plasma, which is commonly used for trauma patients, comes from whole blood donations and from a procedure called apheresis, which extracts only plasma from the donor and returns the rest of the blood.

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 Puget Sound Blood Center, which provides the region's blood and plasma products, is reviewing the emerging information about TRALI and gender differences in plasma, said spokesman Tom Butterworth.

In a statement Monday, he said: "Medical staff are involved in national discussions regarding changes in practice that might be implemented."

The American Association of Blood Banks recently recommended that blood centers and transfusion services have a plan in place by November for dealing with plasma in relation to TRALI, he said.

Doctors at Harborview Medical Center see fewer than five cases of the transfusion-related lung injury a year, said Dr. Ken Steinberg, a pulmonary and critical-care specialist at the trauma center. "In my experience, it's not very common, although sometimes it's hard to diagnose."

Treatment for TRALI usually involves putting the patient on a mechanical ventilator temporarily until the inflammatory reaction abates.

The hospital has not received any specific guidance yet about using only male plasma but said it would take its direction from the Puget Sound Blood Center.

Dr. Thomas Price, medical director and executive vice president of the blood center, is leading a working group of blood centers to develop guidelines for donations with regard to TRALI.

Altogether, the change could prevent about 150 cases of TRALI a year nationally and 15 deaths, estimates Dr. Patricia Kopko, medical director of BloodSource, a California blood bank that made the male-donor shift 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.