Banking on blood conversion: new technology may change the character of the U.S. blood supply - Cover Story

Science News, Jan 11, 1997 by Corinna Wu

Eager donors arrive at a local blood drive, ready to give the gift of life. But before their blood is allowed to flow into a plastic bag through needles plunged into their forearms, they must sit down with a pen and take a test.

The questionnaire-along with biochemical tests on the blood itself-is part of a rigorous screening process that has made the U.S. blood supply one of the safest in the world. As a result of this vigilance, the risks of contracting AIDS or other infectious diseases from a blood transfusion have dropped substantially.

Once that blood reaches the hospital, however, even the most careful initial screening efforts can't protect a patient from getting a fatal transfusion of the wrong blood type-a situation that occurs more often than most people think, says Harvey Klein, who is chief of transfusion medicine at the National Institutes of Health in Bethesda, Md. Sometimes, amid the chaos of an emergency room, or even in less hectic settings, a health care worker misreads a label or a chart and gives the wrong blood to a patient. If blood of type A or B is given to someone with type O blood, for example, the ensuing severe immune reaction can rapidly kill the person.

Improving blood-handling procedures and worker training can forestall such deadly accidents. Some researchers, however, think they may have found a more foolproof solution by chemically converting types A and B red blood cells to the universal type O. That way, any unit of blood cells could be transfused into any patient, removing the need to match blood types.

This innovation would have the added benefits of correcting imbalances in blood type inventories, reducing the amount of blood that gets outdated before it can be used, and cutting the costs of blood distribution. More than 15 years of research into this technique is reaching fruition; hospitals and blood centers may have blood conversion technology by next year.

In any year, as many as 1 in 12,000 units of red blood cells meant for one person is mistakenly given to another, says Klein, but "most of the time, that won't cause any harm, just by luck." Type O blood can be given to anyone, and type A blood presents no problems for someone who happens to be A or AB.

The real danger arises when, for example, a type O patient gets A or B blood or when a type A patient gets B blood. Unfamiliar molecules on the surface of the foreign blood cells trigger the immune system, which kicks into high gear and throws the patient into shock. The kidneys fail, and the depletion of blood-clotting factors causes bleeding "from the nose, ears-every orifice of the body," says Mark Popovsky, chief executive officer of the New England Region American Red Cross.

About 1 in 100,000 people who receive a transfusion dies, including most people who get incompatible blood, Klein says. Although the risk of getting the wrong blood type is fairly low, it spells almost certain death when it happens. "It's sort of like a plane crash. One in 12,000, I've always thought, is a frightening statistic," he adds. Moreover, hospitals may underreport the problem.

Some hospitals try to lessen the chance that a hurried doctor or nurse will make a fatal mistake by stocking only type O blood for emergency rooms and intensive care units, Klein says. This practice, however, can create a shortage of type O blood for the region.

On the other hand, between 5 and 10 percent of A and B blood goes to waste, says Popovsky, simply because hospitals can't use those units within their 42-day shelf life.

To minimize the waste of usable blood, hospitals sometimes ship their surplus to other institutions in the region that need more than they anticipated. Blood also travels between neighboring regional blood centers.

"No one has good data on how frequently blood is moved around," Klein says, but "we know that there is a lot of movement."

Conversion of all blood to type O can address these supply imbalances and reduce the amount of shipping necessary, says Jack Goldstein of the Kimball Research Institute at the New York Blood Center, who is one of the pioneers in the field.

The idea explored by Goldstein and other researchers is to use an enzyme to alter the chemistry of the red cell surface. Chains of sugars, which cover the cell surfaces of the four human blood types-A, B, AB, and O-all have the same basic sequence, with fucose at the end and galactose next in line.

The major distinction between types lies with the sugar that branches off from the galactose. On A cells, that sugar is N-acetylgalactosamine. On B cells, it's another galactose. O cells have no additional sugar at all, while AB blood cells bear a mix of A and B chains. In the United States, about 45 percent of the population has type O blood, 40 percent has type A, 11 percent has type B, and 4 percent has type AB.

A and B cells cannot be transfused into people with O blood because the extra sugar branch stimulates the immune system's antibodies to attack the foreign cells. Clipping off that additional sugar branch from A and B cells transforms them into type O, averting the immune response.