Blood Typing

Blood typing is crucial to giving patients the correct type of blood or blood product, such as plasma or platelets.


All people have a blood type. Blood type can be 1 of 4 types:

  • A.

  • B.

  • AB.

  • O.

Each letter refers to a kind of protein on the surface of red blood cells. For example, the surface of red blood cells in Type A blood has antigens known as A-antigens.


In addition to the ABO typing described above, each blood type is also grouped by its Rhesus factor, or Rh factor. Blood is either Rh positive (Rh+) or Rh negative (Rh-). About 85% of Americans have Rh+ blood. Rhesus refers to another type of antigen, or protein, on the surface of red blood cells. The name Rhesus comes from Rhesus monkeys, in which the protein was discovered.