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", and include the common ABO and Rh antigen systems, as well as many others; thirty-nine major human systems are identified as of July 2019.
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. The genetic basis for most of these antigens lie in 46 red blood cell and six platelet genes. 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, where these and many of the systems are named for patients in whom the corresponding antibodies were first detected.

Blood grouping postulates

Cells

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:
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.

Rare blood types

Different antigens of the various blood group systems are not distributed evenly in a population. Furthermore, different populations have different distributions of specific antigens. Some antigens are rare in a given population or in the whole human population. This can lead to difficulties in finding suitable blood donors for these individuals.
For example, the h/h blood group, also known as Oh or the Bombay blood group, is a rare blood type, while the O blood type is usually the most common blood group in the ABO system.
A comprehensive database of Blood types and their genomic annotations have been compiled which indexes 39 blood groups and 1649 blood antigens.

Blood group systems