Danish researchers have perfected an inexpensive and efficient way to convert types A, B and AB blood into type O, the universal-donor blood that can be given to anyone – an achievement that promises to make transfusions safer and relieve shortages of type O blood.

The team reported Sunday in the journal Nature Biotechnology that they isolated bacterial enzymes that safely remove from red blood cells the sugar molecules that provoke immune reactions in recipients.

Previous studies of type O blood produced from type B by a different method have shown it to be both safe and effective, and the researchers are now conducting clinical trials with the new product.

Mismatching of blood causes at least half of all transfusion-related deaths. And the need for precisely matched blood drives the costly and inefficient process of shuttling blood units between regional blood banks and hospitals to match daily requirements.

“Those issues could be largely resolved if there were a universally transfusible blood supply,” said Doug Clibourn, chief executive of ZymeQuest Inc. in Beverly, Mass., which is developing the technology.

The problem involves sugar molecules on the surface of red blood cells. Type A blood has one set of sugars and type B has another, while type O has none. People with type A blood have antibodies against the type B sugars, people with type B have antibodies against type A, and people with type O have antibodies against both.

If a person receives mismatched blood, the antibodies attack red blood cells, producing a potentially fatal breakdown of red cells.