This is the VOA Special English Health Report.

Scientists may have found a way to reduce shortages of type O blood. Type O is the kind of blood that hospitals most often need. What the researchers are testing is an easier way to make type O blood out of other kinds of blood.

There are four main blood types. Most people are born with one of these four: type A, type B, type AB or type O.

Type O is known as the universal blood type. It can be safely given to anyone. So it is commonly used when a person is injured or sick and has to have a blood transfusion.

Type O is the most common blood group. But the supplies of it available in hospitals and blood banks are usually limited. This is because of high demand. Type O blood is used in emergencies when there is no time to identify the patient's blood type.

Giving A, B or AB to someone with a different blood type, including O, can cause a bad reaction by the person's defense system. Their immune system can reject the blood. This immune reaction can be deadly. For example, people may die if they receive transplanted organs from someone with the wrong blood type.

The difference between blood types is related to whether or not red blood cells contain certain kinds of sugar molecules. These molecules are found on the surface of the cells. They are known as antigens. These antigens are found with type A, B and AB blood but not with type O.

More than twenty-five years ago, scientists found that the antigens could be removed to create universal-type cells. They could be removed with chemicals called enzymes. But large amounts of enzymes were required to make the change.

Now, a report published in Nature Biotechnology describes two formerly unknown bacterial enzymes. The scientists say these enzymes remove the antigens more easily. To find these enzymes, the researchers examined more than two thousand five hundred kinds of bacteria and fungi.

Doctor Henrik Clausen of the University of Copenhagen in Denmark led the study. He worked with researchers from France, Sweden and the United States.

The next step, they say, is to complete safety tests. The team is working with the American company ZymeQuest to test the new method. If it meets safety requirements and is not too costly, it could become a widely used life-saving tool to increase the supply of universal blood.

And that's the VOA Special English Health Report, written by Brianna Blake. For more health news, go to voaspecialenglish.com. I'm Steve Ember.