Every time a person's blood is analyzed under a microscope distinct blood differences are visible. In the early 20th century, a scientist named Karl Landsteiner classified blood according to those distinct differences. Namely, Landsteiner observed two distinct chemical molecules present on the surface of the red blood cells. He labeled one molecule "A" and the other molecule "B".
Blood Types
A blood type is defined as the classification of blood that is based on the presence or absence of inherited antigenic substances on the surface of red blood cells (RBCs). Normally, a number of related blood types constitute a blood group system, such as the Rh or ABO system. The frequencies of the ABO and Rh blood types vary from population to population.
- Blood Type A - If the red blood cell has only "A" molecules on it.
- Blood Type B - If the red blood cell has only "B" molecules on it.
- Blood Type AB - If the red blood cell has a mixture of both "A" & "B" molecules.
- Blood Type O - If the red blood cell has neither "A" or "B" molecule.
There are eight different common blood types. Normally, they are determined by the presence or absence of certain antigens, which are substances that can trigger an immune response if they are foreign to the human body. Since some antigens can trigger a patient's immune system to attack the transfused blood, safe blood transfusions significantly depend on careful blood typing and cross-matching.
Is There a Universal Blood Donor Type?
At one time, type O negative blood was considered the universal blood donor type. Furthermore, this indicated that anyone, regardless of blood type, could receive type O negative blood without risking a transfusion reaction. However, it's now known that even type O negative blood may have antibodies that can cause seevere reactions during a transfusion. And blood transfusions in general carry some risk of complications.
Blood may be classified as one of these four types:
- Type A
- Type B
- Type AB
- Type O
Blood is also classified by rhesus (Rh) factor. This particular factor refers to a specific red blood cell antigen in the blood. In case your blood has the antigen, you're Rh positive. If your blood lacks the antigen, you're Rh negative.
In an ideal situation, blood transfusions are done with donated blood that's an exact match for type and Rh factor. Even then, small samples of the recipient's and donor's blood are mixed to check compatibility in a process known as cross matching.
In an emergency, type O negative red blood cells may be given to anyone. This is especially the case if the situation is life-threatening or the matching blood type is in short supply.
Donation Facts
- The average adult has 10-12 pints of blood.
- Someone needs blood every two seconds in the U.S.
- 40,000 pints: Amount of donated blood used each day in the U.S. and Canada
- Through a process of separating blood into its individual parts, a single unit of blood can help extend the lives of as many as three people.
- After blood is drawn, at least 12 tests are performed on each donation in order to ensure safe blood is available.
- There is no substitute for blood, when a patient requires blood, there is only one source - a blood donor.
- You are able to donate whole blood and red cell + plasma apheresis every eight weeks.
- You are able to donate platelet apheresis every two weeks.
- You are able to donate red cell aphereisis every 16 weeks.
There’s no end to the benefits of donating blood for those who need it. Namely, one donation can save as many as three lives, and someone in the United States needs blood every two seconds. It turns out that donating blood doesn’t just benefit recipients. There are health benefits for donors, too, on top of the benefits that come from helping others.
