1 Your plasma has antibodies that attack both type A and type B blood. 2  About 44% of people (44 in 100) in the U.S. have type O blood, with 7% having O-negative (O-) blood and 37% having O-positive (O+) blood. 3  Both the A and B antigens, you have type AB blood.
http://www.webmd.com/a-to-z-guides/blood-type-test
Human blood is typed by certain markers (called antigens) on the surface of red blood cells. Blood type may also be done to see if two people are likely to be blood relatives. The most important antigens are blood group antigens (ABO) and the Rh antigen, which is either present (positive, +) or absent (negative, -). So the two most common blood type tests are the ABO and Rh tests.
http://www.webmd.com/a-to-z-guides/blood-type-test
Blood is also classified by rhesus (Rh) factor, which refers to a specific red blood cell antigen in the blood. If your blood has the antigen, you're Rh positive. If your blood lacks the antigen, you're Rh negative. Ideally, blood transfusions are done with donated blood that's an exact match for type and Rh factor.
http://www.mayoclinic.org/tests-procedures/blood-transfusion/expert-answers/universal-blood-donor-type/FAQ-20058229
Even then, small samples of the recipient's and donor's blood are mixed to check compatibility in a process known as crossmatching. In an emergency, however, type O negative red blood cells may be given to anyone — especially if the situation is life-threatening or the matching blood type is in short supply. With.
http://www.mayoclinic.org/tests-procedures/blood-transfusion/expert-answers/universal-blood-donor-type/FAQ-20058229
Blood type (or blood group) is determined, in part, by the ABO blood group antigens present on red blood cells. A blood type (also called a blood group) is a classification of blood based on the presence or absence of inherited antigenic substances on the surface of red blood cells (RBCs). These antigens may be proteins, carbohydrates, glycoproteins, or glycolipids, depending on the blood group system.
https://en.wikipedia.org/wiki/Blood_type
The ABO test shows that people have one of four blood types: A, B, AB, or O. If your red blood cells have: 1  The A antigen, you have type A blood. 2  The B antigen, you have type B blood. 3  Neither the A nor B antigen, you have type O blood. 4  Both the A and B antigens, you have type AB blood.
http://www.webmd.com/a-to-z-guides/blood-type-test
At one time, type O negative blood was considered the universal blood donor type. This implied that anyone — regardless of blood type — could receive type O negative blood without risking a transfusion reaction. However, we now know even type O negative blood may have antibodies that cause serious reactions during a transfusion. There are four types of blood.
http://www.mayoclinic.org/tests-procedures/blood-transfusion/expert-answers/universal-blood-donor-type/FAQ-20058229
The ABO test shows that people have one of four blood types: A, B, AB, or O. If your red blood cells have: 1  The A antigen, you have type A blood. 2  The liquid portion of your blood (plasma) has antibodies that attack type B blood.
http://www.webmd.com/a-to-z-guides/blood-type-test
Some of these antigens are also present on the surface of other types of cells of various tissues. Several of these red blood cell surface antigens can stem from one allele (or an alternative version of a gene) and collectively form a blood group system.
https://en.wikipedia.org/wiki/Blood_type
O Negative. As an O Negative blood donor you have a particularly unique opportunity to help people in emergency situations. O Negative blood cells are called “universal” meaning they can be transfused to almost any patient in need, and only 6.6% of the population has O Negative blood. In the event of an emergency, trauma patients and accident victims are given a fighting chance at life due to O Negative blood transfusion. You may hear that “O Negative blood is the type they carry on the medical helicopters”. This is often the case when there is no time to ask questions. Additionally, O Negative red blood cells are safest for newborn infants with under-developed immune systems.
http://thebloodconnection.org/about-blood/blood-education/blood-types/o-negative/
which blood type is called universal donor
O negative blood is type of blood that is universal donor.