A new process undergoing final testing may rid donated blood of virtually all viruses and bacteria, bringing a new level of safety to blood transfusions. The process, which uses chemicals that bind the genetic material of pathogens, could eliminate the rare cases of HIV transmission through transfusions not already caught by testing blood and screening donors. Most important, it could eliminate any other pathogens, including ones not yet identified.

"No matter what the bug is, you can kill it without even knowing it's there," said Dr. Stephen T. Isaccs, president of Cerus Corporation, the company leading the development of the technique, called pathogen inactivation. Cerus hopes to win approval in the United States for use on platelets early next year.

"One of the things we will have to be certain of is that we are not trading a very tiny risk of viral infection for another risk of adding chemicals to the blood," said Dr. Jerry Squires, chief scientific officer of the American Red Cross. Equally important will be to show that the processes do not harm the ability of the blood cells to do their jobs.

Pathogen inactivation takes advantage of the fact that the parts of blood given in transfusion -- red blood cells to carry oxygen, platelets to help the blood clot and plasma for clotting and other purposes -- do not contain DNA or RNA. But bacteria and viruses do. Binding or gumming up DNA or RNA would kill pathogens, while, in theory at least, leaving the blood itself unharmed. However, it may also allow the chemicals to bind to DNA in patients who get the transfusions.

The greatest benefit of pathogen inactivation may be the insurance it provides against a new pathogen. "I can tell you as I sit here today that if an agent like HIV emerged next week, we would not be in any better position to deal with it now than we were in 1982," said Dr. Harvey G. Klein, head of the department of transfusion medicine at the National Institutes of Health. He and others believe that the American public has been willing to spend whatever it takes to eliminate even marginal risks of infection. That factor, plus fear of being sued, makes it highly likely that pathogen inactivation will be widely adopted.

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