Researchers find ways to prolong shelf life of blood platelets

WASHINGTON -- The lives of many cancer patients are saved by the transfusion of platelets, but there is a chronic shortage of these fragile blood-clotting components because of spoilage. A new technique may double the shelf life of platelets and create a more reliable supply, researchers say.

In a study appearing in the journal Science, Harvard University researchers have demonstrated that adding a bit of sugar to isolated blood platelets can allow them to be refrigerated and usefully preserved for at least 12 days.

That more than doubles the shelf life of the current technique used, 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.

Essential action

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 blood stream. That means 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.

2 million patients

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 pints to six pints of donated blood.

Once they are separated, platelets are very fragile. If they are refrigerated, as is whole blood, 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 University 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, a type of sugar.

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.