Type O blood is the universal blood type and is the only blood type that can be transfused to patients with other blood types. Type O blood consists of O+ and O- blood. Almost 40% of the population has O+ blood, but Only about 7% of all people have Type O negative blood. So Type O blood is the most common blood type, and also the most used.
On the contrary, patients who have type AB blood are considered universal recipients because they can receive blood or blood products from any other blood type. However, these patients may only donate their blood to patients who have AB blood.
Type O blood (called type zero in some countries) has neither the A or B antigen and therefore, type O negative blood can be given to anyone. Persons with type O negative blood are referred to as “universal donors”.
Type O negative blood is the preferred type for accident victims and babies needing exchange transfusions. There is always a need for Type O donors because their blood may be transfused to a person of any blood type in an emergency.
Cutting-edge enzyme transfusion technology holds the promise that bacterial enzymes be able to safely convert A, B, and AB blood to the universally useful type O.
After sifting through more than 2,500 compounds from bacteria and fungi, biologists led by Henrik Clausen of the University of Copenhagen in Denmark, have found a pair of enzymes that can rapidly and efficiently break down the A and B molecules, leaving cells as type O. One came from the bacteria Elizabethkingia meningosepticum, and the other from the species Bacteroides fragilis.
I myself has the type O blood, but I am not sure if negative or positive. Six years ago when studying in a Chinese university, we are advised to donate blood as a national campaign to raise the storage of national blood bank. But an operation in one of my nostrils right before the donating date prevented me doing so.
Source: Universal Blood Type @ NewsBlogPk.com; America Red Cross
Enzymes may allow universal blood transfusions @ Cosmosmagazine