WEDNESDAY, Aug. 18, 2004 (HealthDayNews) -- A generation ago, one in every 100 units of donated blood in the United States passed HIV or the hepatitis C virus to an unknowing recipient.
Thanks to more sophisticated screening, namely nucleic acid amplification testing, that rate has plummeted.
Even with all the testing, there's a window of time during which infectious agents can slip through undetected. Researchers, however, continue to fine-tune both the blood and tissue donation process to further reduce that rate.
Two studies appearing in the Aug. 19 issue of the New England Journal of Medicine review the risks of transmitting various viruses through both blood and tissue donations.
According to the authors of one article, the U.S. blood supply was made vastly safer by the introduction of nucleic acid amplification testing in 1999.
This technique allows for testing before people have developed antibodies to viruses such as HIV and hepatitis C, which is what older tests screened for, said Dr. Jesse Goodman.
"This [nucleic acid amplification] culminated in an extraordinarily high level of safety," said Goodman, director of the U.S. Food and Drug Administration's Center for Biologics Evaluation and Research, and an author of an accompanying editorial in the journal.
The study authors estimate the introduction of minipool nucleic acid amplification testing -- which tests 16 to 24 units of blood at a time -- has helped prevent the transmission of about five HIV infections and 56 hepatitis C infections annually. The residual risk of transfusion-transmitted HIV and hepatitis C has been lowered to about one per 2 million blood units, according to the researchers.
Nucleic acid testing is just now being introduced for tissue donations, where the likelihood that an undetected infection will get passed on is higher than for blood donations.
"Companies are just now getting it licensed for use with tissue donors," said Michael Strong, senior author of the second study and executive vice president of Puget Sound Blood Center/Northwest Tissue Center in Seattle. "There's an opportunity to reduce the risk here."
The authors estimate the current probability of passing on various viruses from a tissue donation is one in 55,000 for HIV; one in 34,000 for hepatitis B; one in 42,000 for hepatitis C; and one in 128,000 for human T-lymphotropic virus.
There are many fewer tissue donors than blood donors. But, while a blood donation may go to three or four people, a tissue donation could conceivably go to 100 people. One recent organ donor in the United States transmitted rabies to four people, all of whom died.
"Nucleic acid testing will have a benefit in preventing some of the rare transmission of these viruses," Goodman said.
Thanks largely to new testing methods, blood and tissue donations are "safer than ever," he added.
But those are only the known risks.
"As with West Nile, we constantly face new concerns," Goodman noted. "There are always going to be challenges that are new. There's evidence from the U.K. that mad cow disease can potentially be transfusion-transmitted."
"Fortunately, there are not a lot of human cases. We're already taking measure there to try to reduce donation by donors who have potentially higher exposure to that agent [mad cow] from having lived in areas where it's more common. We don't have a great scientific understanding or testing available for that yet."
Will donated blood and tissue ever be completely safe?
"I don't think any tissue or blood that's derived from a living human or other creature can ever be guaranteed free of some unknown or unsuspected infectious agent," Goodman said. "With the right kind of thinking ahead, we are really poised to be able to respond more quickly. On the other hand, you can't always see everything coming."
More information
Visit the American Association of Blood Banks for more on blood supply safety.
