Scrubbing The Blood Supply
William "Cappy" Young, a 53-year-old forklift operator from Petersburg, Va., entered the hospital last March for routine surgery to improve circulation in his legs. The surgery was successful, but Young emerged with a far more serious problem. He received a unit of blood that had somehow slipped through the tough screening protocols that have made the U.S. blood supply safer than it has ever been. The blood was contaminated with the AIDS virus. Young is now HIV-positive, one of the 50 Americans each year who contract HIV through transfusions. "My doctor told me the blood was tested so thoroughly that there was virtually no chance of it being infected. I put my faith in the doctor," Young says.
Every pint of blood donated in the U.S. is subjected to nine different tests to cull contaminated donations. But, as Young's case shows, despite extensive scrutiny disease-carrying blood sneaks into the system. That's because the current tests don't look for infectious agents directly. Instead, they detect antibodies, which the body's immune system makes in response to infection. Because it can take weeks or months for antibodies to build up in the blood, newly infected donors sometimes pass along a virus that doesn't show up on antibody-screening tests.
Researchers are now experimenting with three technologies aimed at further improving the safety of the blood supply. The first, called nucleic acid testing, is so powerful it can detect the presence of fewer than 30 infectious particles in the bloodstream. Such tests will help cut the spread of infections, but they will not solve all the problems. Unknown threats linger on the horizon, and there are some pathogens--such as emerging variants of hepatitis--for which no test yet exists.
To deal with those infections, researchers have developed a second set of technologies aimed at cleaning the blood of such disease particles as hepatitis C, HIV, or syphilis. A third technology filters blood to remove infectious agents before they are passed along.
While these technologies will pay off in patient health, they come at a hefty cost: Nucleic acid testing and filtration together are expected to drive up the price of blood from about $80 to as much as $120 a pint. But blood bankers say the expense is worth it. "We'll do whatever we can to increase the safety of our blood supply," says Dr. Richard J. Davey, chief medical officer of the American Red Cross.
Blood is a complex biological substance that can be separated into three fractions: red blood cells, platelets, and plasma. Each year, doctors transfuse more than 23 million units--or three million gallons--of blood components. According to a recent New England Journal of Medicine report, the risk of developing HIV from one pint of blood is 1 in 675,000; the risk of HTLV, a virus that causes leukemia and progressive neurologic disorders, is 1 in 641,000; and the risk of hepatitis C is 1 in 100,000.
These numbers seem small, but physicians warn that such risks are cumulative. "Almost no one receives just one unit of blood when transfused, and the more blood a person receives, the greater his or her chance of being infected," says Dr. Bernard Horowitz of the New York Blood Center. In fact, the real risk of contracting a viral disease may be more like 1 in 5,000--which is 1,000 times greater than the odds of dying in an airplane crash. Put another way, if airlines were allowed to set an "acceptable safety standard" equivalent to that of the blood supply, there would be at least one fatal crash a month in the U.S. "Errors and accidents in the blood supply remain a safety problem that can be reduced" says Representative Thomas J. Bliley Jr. (R-Va.), chairman of the House Commerce Committee.
Nucleic acid testing can help reduce those errors and accidents. The test relies on specially designed genetic "probes" that recognize and latch on to any viral particles in the blood, even if they're present in minute quantities. "It's basically like using a huge magnifying glass to detect small numbers of viruses," says Melissa E. McMillan of America's Blood Centers (ABC), an organization of blood banks. Conventional antibody tests won't pick up HIV contamination until an average of 22 days after infection. But theoretically, nucleic acid testing can detect contamination only 11 days after infection. Likewise, nucleic acid testing for hepatitis C can cut the detection time after infection from 82 days to 23 days. So far this year, blood centers using nucleic acid testing have caught 16 units contaminated with hepatitis C out of more than 5 million that tested negative with conventional methods.
NO RISK? Both the American Red Cross and the American Blood Centers, which together distribute 93% of the nation's blood supply, are already employing nucleic acid testing on an experimental basis. The Food & Drug Administration is expected to approve it later this year or early in 2000. "It's a powerful technique," says James MacPherson, the executive director of ABC. It "helps eliminate the last residual risk of HIV in the blood supply."
Two California companies, Roche Molecular Systems Inc. and Chiron Corp., are vying for the $200 million market for nucleic acid testing. Chiron's technology is capable of processing 600 samples a day, and by the end of the year should be able to handle more than 1,000. Such speed is needed if nucleic acid testing is to screen the 40,000 donations that blood centers get each day.
If nucleic acid tests promise to reduce the risks substantially, another technology called viral inactivation has the potential to eliminate them. Researchers say viral inactivation can disable any bacteria or viruses in the blood without affecting the health of the blood cells. So powerful is the technology that in October the American Red Cross made viral inactivation of plasma a requirement for its distributors.
Various techniques can be used to inactivate viruses. V.I. Technologies Inc., of Melville, N.Y., has the only process approved by the Food & Drug Administration. The company, usually called Vitex, uses detergents to break up viruses hiding in plasma. The company recently joined with Pentose Pharmaceuticals Inc., a biotech company based in Cambridge, Mass., to develop compounds that neutralize pathogens in red cells and platelets.
Meanwhile, Cerus Corp. of Concord, Calif., has created two inactivators, one for platelets and plasma and a second for red cells. They work by slipping into a virus' genes and preventing the virus from reproducing. Dr. Edward L. Snyder, director of Yale University's blood bank, has been testing Cerus' platelet inactivator and he's impressed. "In my judgment, it gives a better product. We lived through one AIDS crisis, and we can't afford another. This technology has the potential to prevent that from happening again."
99.9% PURE. As Vitex and Cerus battle to develop better inactivators, Pall Corp. is working on filtration. Pall's technology, called leukocyte reduction, is basically a high-tech method of removing white blood cells, which may cause high fevers and infections in transfusion recipients. White cells can harbor cytomegalovirus, HIV, mad-cow disease, and other dangerous agents. Pall's filters get rid of more than 99.9% of all white cells in a unit of blood.
A growing number of countries, including Canada, Britain, France, and Portugal, have mandated white-cell filtration for blood supplies. Last year, FDA advisors unanimously recommended the procedure for use in the U.S. The FDA is expected to approve the technique formally in December. Meanwhile, many U.S. physicians and hospitals have already opted to use only filtered blood. "I realized that if a member of my family required a transfusion, I would prefer that it be filtered. Why shouldn't I provide the same level of quality for my patients?" says Dr. Anne T. Thomas, who runs the Vanderbilt University Medical Center Blood Bank.
Canada and Europe have much more aggressive stances on blood safety than the U.S. The Canadian Red Cross is still reeling from a 1980s scandal in which some 60,000 transfusion patients contracted hepatitis C from contaminated blood. Haunting memories of widespread AIDS contamination in France, coupled with the threat of mad-cow disease, have prompted many European countries to mandate the use of nucleic acid testing and white-cell filtration. Nucleic acid testing is expected to add $10 to the cost of every pint of blood, while filtration adds an additional $30. Viral activation won't come cheap, either: It's expected to double or triple the cost of blood.
Even so, America's blood banks are likely to adopt these tests as soon as they become available. The public will demand them, because even one more Cappy Young would be too many.
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