What Is a Blood Type and Do All Humans Have the Same Type?
A blood type (also called a blood group) is a classification of blood based on the presence and absence of antibodies and also 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. 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. Blood types are inherited and represent contributions from both parents. A total of 36 human blood group systems are now recognized by the International Society of Blood Transfusion (ISBT).
The two most important ones are ABO and the Rh blood group systems; they determine someone’s blood type (A, B, AB and O, with +, − or null denoting RhD status) for suitability in blood transfusion. Thus, in addition to the ABO antigens and Rh antigens, many other antigens are expressed on the RBC surface membrane.
For example, an individual can be AB, D positive, and at the same time M and N positive (MNS system), K positive (Kell system), Lea or Leb negative (Lewis system), and so on, being positive or negative for each blood group system antigen. Many of the blood group systems were named after the patients in whom the corresponding antibodies were initially encountered.
Although all human blood looks the same when seen under a microscope, we do not all have the same type of blood. Some substances, found in the red corpuscles and in the plasma in which they float, vary from individual to individual. When one person’s blood is transfused into another, these differences must be taken into account to avoid incompatibility between the recipient’s and donor’s blood.
Perhaps you already know, which blood group you belong to: A, B, AB, O, Rhesus + Rhesus + (Rhesus Positive), or Rhesus – (Rhesus Negative). But do you know that people with blood group A have the agglutinogen A in their red Corpuscles, and agglutininogen B in their plasma. (Agglutinogen means any substance that, when present in the bloodstream, can cause the production of specific antibodies or agglutinins).
People belonging to blood group B have agglutinogen B in their red corpuscles and agglutinin (alpha) in their plasma. If you mix blood A with blood B in a test-tube, you will see that the red corpuscles stick to each other, form clumps and are destroyed. Imagine the catastrophe this would cause in incompatible blood transfusion-many of the recipient’s red corpuscles would be destroyed; they could clump together and block the blood vessels, with potentially fatal results.
People with blood group AB have no agglutinins in their plasma. They can therefore receive blood from group A, B, O and, of course, AB. People with group O have red corpuscles without agglutinogens, but as their plasma contains the two agglutinins, they can only receive blood from group O. They are, however, able to give blood to patients of group A, B, AB, and O. Group O is known as the ‘universal donor’, group AB as the ‘universal recipient’.
The red corpuscles often contain another agglutinogen called ‘Rhesus’ (Rh), or ‘the Rhesus factor’. This was discovered whilst carrying out experiments on Rhesus monkeys. The red blood cells of most humans contain the Rhesus factor. Those, which do not are said to be Rhesus negative.
People without the Rh factor in their corpuscles may react to an initial blood transfusion by producing anti-Rhesus agglutinins. This may cause problems, such as agglutination (clumping together) and destruction of the red corpuscles after subsequent transfusions.
You can see that it is extremely important to know the exact blood group of a person before giving a blood transfusion. There are diseases, which require repeated blood transfusion, when it is necessary to find a much closer match between the recipient and the donor. The Kell system divides blood into two groups: Kell + for those with the agglutinogen Kell, and K- for those without this agglutinogen. It is the most frequently used system after the A, B, O and Rhesus system, but they’re others: for example, Diego, Duffy, and Lutheran Lewis.