When a person's blood is analyzed under a microscope distinct blood differences are visible. In the early 20th century, an Austrian scientist named Karl Landsteiner classified blood according to those differences. 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".
A blood type (also called a blood group) is defined as the classification of blood based on the presence or absence of inherited antigenic substances on the surface of red blood cells (RBCs). A series of related blood types constitutes 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.
There are eight different common blood types, which 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 depend on careful blood typing and cross-matching. There are 4 major blood groups determined by the presence or absence of two antigens (A and B) on the surface of red blood cells:
|Common Blood Types|
|A||Has only A antigen on red cells (and B antibody in the plasma)|
|B||Has only B antigen on red cells (and A antibody in the plasma)|
|AB||Has both A and B antigens on red cells (but neither A nor B antibody in the plasma)|
|O||Has neither A nor B antigens on red cells (but both A and B antibody are in the plasma)|
In addition to the A and B antigens, there is a third antigen called the Rh factor, which can be either present (+) or absent ( - ). In general, Rh negative blood is given to Rh-negative patients, and Rh positive blood or Rh negative blood may be given to Rh positive patients.
Blood types are very important when a blood transfusion is necessary. In a blood transfusion, a patient must receive a blood type compatible with his or her own blood type. If the blood types are not compatible, red blood cells will clump together, making clots that can block blood vessels and cause death.
If two different blood types are mixed together, the blood cells may begin to clump together in the blood vessels, causing a potentially fatal situation. Therefore, it is important that blood types be matched before blood transfusions take place. In an emergency, type O blood can be given because it is most likely to be accepted by all blood types. However, there is still a risk involved.
|Compatible Blood Type Donors|
|Blood Type||Donate Blood To||Receive Blood From|
|A+||A+ AB+||A+ A- O+ O-|
|O+||O+ A+ B+ AB+||O+ O-|
|B+||B+ AB+||B+ B- O+ O-|
|A-||A+ A- AB+ AB-||A- O-|
|B-||B+ B- AB+ AB-||B- O-|
|AB-||AB+ AB-||AB- A- B- O-|
It is easy and inexpensive to determine a person's ABO type from a few drops of blood. A serum containing anti-A antibodies is mixed with some of the blood. Another serum with anti-B antibodies is mixed with the remaining sample. Whether or not agglutination occurs in either sample indicates the ABO type. It is a simple process of elimination of the possibilities. For instance, if an individual's blood sample is agglutinated by the anti-A antibody, but not the anti-B antibody, it means that the A antigen is present but not the B antigen. Therefore, the blood type is A. Blood type is inherited, just like eye color. The chart below shows the possible blood type of a child according to their parents blood group:
|Inherited Blood Type|
In most cases, blood typing is not conclusive when attempting to determine, include or exclude an individual as the parent of a child or children. While blood types are 100% genetically inherited, the environment potentially can determine which blood types in a population will be passed on more frequently to the next generation. It does this through natural selection. Specific ABO blood types are thought to be linked with increased or decreased susceptibility to particular diseases.
RH factor in blood types stands for "Rhesus Factor". Blood tests were performed on Rhesus monkeys and the Rh+ and Rh- factors were isolated. An antigen found in the red blood cells of most people: those who have Rh factor are said to be Rh positive (Rh+), while those who do not are Rh negative (Rh-). What about the meaning of RHD- Rh blood group, D antigen . The rhesus complex is not just one antigen, but several, when someone is told to be Rh+, it usually refers to the D antigen (one of the components of the Rh complex), because it's the most common, and the easiest to identify, however it's not the only one.
According to the American Red Cross the rarest is AB(-), present in 1% of the Caucasians, in African Americans it is even rarer. B(-) and O(-) are also very rare, each accounting for less than 5% of the world's population. Some people with rare blood types bank their own blood in advance of surgical procedures to ensure that blood is available to them.
A blood type is considered rare if fewer than 1 in 1,000 people have them. One of the rarest blood types in the world is Rh-null, which lack any antigens in the Rh system. There are only 9 active donors in the community of rare blood donors that have Rh-null blood. Rh-null is considered a universal blood for anyone with a rare blood type within the Rh system. However, anyone who has Rh-null blood can only receive Rh-null blood in a transfusion.
See our list for other amazing facts about human blood and the heart.
The Eat Right for Your Type diet encourages people to eat certain foods and avoid others based on their blood type A, B, AB, or O. The Diet is Based on:
NOTE: Critics cite a lack of published evidence backing D'Adamo's blood type-based diet plan.
Legend has it that blood type tells about personality.
In Japan, it's widely believed that blood groups predict personality traits - from temperament to compatibility, to what kind of lover you are to what type of foods you should be eating. For instance: