Harvard University researchers report this week in the journal Science that laboratory tests show that putting a small amount of galactose, a type of sugar, into isolated platelets allows the blood components to be refrigerated and usefully preserved for at least 12 days.
That more than doubles the shelf life of the current routine, which is to store the platelets at room temperature for only five days. Because of spoilage, more than 25 percent of all platelets taken from donated blood must be discarded. Extending the shelf life of platelets would significantly improve the supply, experts say.
"If this proves out in clinical trials, this would be an important advance in transfusion medicine," said Dr. Louis M. Katz, medical director of the Mississippi Valley Regional Blood Center in Davenport, Iowa. Katz is president of America's Blood Centers, an organization that collects about half the blood donated in the United States.
Platelets play a central role in forming blood clots, an essential action to prevent uncontrolled bleeding in the body. Platelets are made in the bone marrow and typically live 10 to 12 days in the bloodstream, so the body has to constantly make more platelets to replace those that die.
Many cancer and leukemia patients are unable to naturally replace their platelets. Aggressive chemotherapy used to treat many cancers can cause the bone marrow to shut down, leaving these patients, at least temporarily, without natural platelet replacement.
As a result, about 2 million patients a year require platelet transfusions to avoid possibly lethal, uncontrolled bleeding.
To get enough platelets for a single treatment, blood centers have to process four to six pints of donated blood.
Once they are separated, platelets are very fragile. If they are refrigerated, as whole blood is, the platelets undergo a chemical change that makes them the target of macrophages, one of the body's immune cells. When chilled platelets are transfused, they are engulfed and killed by the macrophages. For this reason, platelets are stored at room temperature and become useless after five days.
Room temperature storage also causes bacteria to grow in warm platelets. Refrigeration, if it was possible, would prevent this.
A team of researchers at Harvard and Brigham and Women's Hospital in Boston have found that platelets can be refrigerated and remain useful for about 12 days if they add a small amount of galactose.
Dr. Karin M. Hoffmeister, first author of the Science study, said macrophages attack chilled platelets because the immune cell targets another type of sugar on the surface of the transfused cell. Adding galactose covers up that other sugar and protects the platelets from the macrophages.
"It is kind of a trick that prevents the removal of platelet cells by the macrophages," Hoffmeister said.
The technique was tested in mice and the researchers found that the chilled, sugarcoated platelets lasted longer and performed better than platelets that had been kept at room temperature.
In test tube studies, said Hoffmeister, human platelets also lasted longer.
"The same action that we found in mouse platelets seems to happen in human specimens," she said. "Human platelets (mixed with galactose) can be stored up to 12 days in a tube at (39 degrees) and they still function."
Hoffmeister said the next step is to test the viability of sugarcoated, chilled platelets in laboratory primates, such as monkeys or apes. If the technique proves successful there, she said, the research team will apply to the Food and Drug Administration to test the system on humans. That could take two to three years, she said.
Katz said that to completely process a dose of platelets from donated blood takes 24 hours to 48 hours. Since the platelets are only good for five days, this leaves only three days to distribute the dose, sometimes across the country, and to get it to a patient who needs it. As a result, he said, about one-fourth of all platelet doses are wasted.
Extending viability to 12 days, he said, means "the problem of platelets outdating before they are transfused will become a tiny problem in comparison to what it is now. This could be very, very important."
By Paul Recer