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Information on Different Blood Types

by Dr. Mary Williams, R.N. D.C.

Blood is essentially the same, from one human being to another; it is always composed of red and white blood cells and plasma. However, blood does vary among people in two critical respects: the presence or absence of antigens and the presence or absence of a protein called "Rh factor" on the red blood cells. An individual has blood of one of the four eight resulting categories, or "blood types," for the duration of his or her lifetime. With the advent of blood transfusions in medicine, identifying an individual's blood type became critically important. Certain blood types can safely be introduced into the circulatory system of individuals with other blood types. However, certain blood types cannot be mixed together.


The 'O' blood type is also commonly known as the "Universal blood type" or the "universal donor," because it contains neither A nor B antigens on the red blood cells. However, there are both A and B antibodies in the blood plasma. As a result, this type of blood can be used as an infusion to give to individuals with any blood type. Nonetheless, due to the presence of antibodies in the blood plasma, the term "universal blood type" is now somewhat contested. Blood type-related complications in blood transfusions may still occur if there is an issue with the 'O' type blood's antibodies. Given the patterns of genetic inheritance that determine blood type, 'O' type blood is relatively uncommon, compared with A or B type blood. 'O'-type blood may be further divided into Rh+ and Rh-, also known as O+ and O-. This distinction refers to the presence or absence of Rh proteins on the red blood cells.


The 'A' blood type contains 'A' type agglutinogens, a type of antigen. These antigens are present in the red blood cells of the 'A'-type blood. Individuals with the 'A' blood type have the 'B'-type antibody in their blood plasma. In addition, the red blood cells of 'A'-type blood may contain Rh proteins on the cell surface. If this Rh protein is present, the blood is categorized as 'A+'. If it is lacking, the blood is 'A-'. With regard to blood transfusions, individuals with 'A' blood type may donate their blood to individuals with 'A' or 'AB' blood types. Patients with Rh+ blood may receive either Rh+ or Rh- blood, but not vice-versa. (If you have Rh- blood, you can only receive a transfusion of Rh- blood.)


'B' type blood is characterized by the presence of 'B'-type antigens in the red blood cells and by 'A'-type antibodies in the plasma. As in the case of 'A' or 'O'-type blood, an individual with a 'B' blood type may be Rh+ or Rh-, depending on whether there are Rh proteins on the red blood cells. Individuals with 'B' blood type may donate blood for use by patients with either 'B' or 'O' blood types.


The 'AB' blood type, also known as the "universal receiver" blood type, contains both the A and B antigens on the red blood cells, but contains neither A or B antibodies in the plasma. As a result, individuals with the 'AB' blood type may receive transfusions of any kind of blood. However, they can only donate their blood for use by other individuals of the 'AB' blood type. The 'AB' blood type is produced when the alleles, or genetic indicators, of the mother and father are each 'A' and 'B'. Instead of one type dominating the other, and causing the child to be either 'A' or 'B' type, they are both present, to produce 'AB'-type blood. Despite the common use of the term "universal receiver" for AB type blood, the name may be somewhat deceiving. In addition to the A and B antigens that determine a person's blood type by the ABO system, human blood actually contains hundreds of antigens. In most cases, the presence of these other antigens is quite uniform throughout the human population. However, in some unusual cases, an individual may be lacking a particular antigen. In these rare cases, even an individual with an 'AB' blood type may not be able to receive a transfusion of 'AB' blood. As with 'A', 'B' or 'O' blood types, the 'AB' blood type may be either Rh+ or Rh-.