Human blood group systems

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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; 38 major human systems are identified as of August 2019.^[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 46 red blood cell and six 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 Le^a or Le^b 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[edit]

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Cells[edit]

Platelets amongst red blood cells

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

• Red blood cells carry oxygen
• White blood cells fight infection
• Platelets stop bleeding in injuries

Antigens[edit]

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.

Rare blood types[edit]

Different antigens of the various blood group systems are not distributed evenly in a population.^[4] 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,^{[5][citation needed]} 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^[6] which indexes 39 blood groups and 1649 blood antigens.

Blood group systems[edit]