Human blood group systems

The term human blood group systems is defined by International Society of Blood Transfusion as systems in the human species where cell-surface antigens—in particular, those on blood cells—are "controlled at a single gene locus or by two or more very closely linked homologous genes with little or no observable recombination between them",[1] and include the common ABO and Rh (Rhesus) antigen systems, as well as many others; thirty-five major human systems are identified as of November 2014.[2]

In addition to the ABO and Rh systems, the antigens expressed on blood cell membrane surfaces include 346 red blood cell antigens and 33 platelet antigens, as defined serologically.[3][better source needed] The genetic basis for most of these antigens lie in 45 red blood cell and 6 platelet genes.[citation needed] An individual, for example, can be AB RhD positive, and at the same time M and N positive in the MNS system, K positive in the Kell system, and Lea or Leb positive in the Lewis system,[citation needed] where these and many of the systems are named for patients in whom the corresponding antibodies were first detected.[citation needed]

Blood grouping postulates



Blood is composed of cells suspended in a liquid called plasma. Suspended in the plasma are three types of cells:


The most common type of grouping is the ABO blood group system. The varieties of glycoprotein and glycolipid coating on red blood cells divides blood into four groups:

  • A (A oligosaccharide is present)
  • B (B oligosaccharide is present)
  • AB (A and B oligosaccharides are present)
  • O (neither A nor B, only their precursor H oligosaccharide present)

Another antigen, the Rh factor, plays an important part in the grouping of blood. If this is present, the particular blood type is called Rh-positive. If it is absent, it is called Rh-negative.