The term human blood group systems is defined by International Society of Blood Transfusion as systems, such as ABO and D antigen, where blood cell surface antigens 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", Thirtyfive human systems have been identified as of November 2014. 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 lay in 45 red blood cell and 6 platelet genes. An individual, for example, can be AB and D 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.
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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 (either uppercase or lowercase) grouping. The varieties of glycoprotein coating on red blood cells divides blood into four groups:
There are subtypes under this grouping (listed as A1, A2, A1B or A2B…) some of which are quite rare. Apart from this there is a protein which plays an important part in the grouping of blood. This is called the Rh factor. If this is present, the particular blood type is called positive. If it is absent, it is called negative. Thus we have the following broad categories:
Rare blood types
In the "ABO" system, (and Rhesus D system) all blood belongs to one of four major groups: A+/−, B+/−, AB+/−, or O+/−. The presence (+) or absence (−) of the RhD (Rhesus D) antigen is indicated by the plus or minus following the ABO type. But there are more than two hundred minor blood groups that can complicate blood transfusions. These are known as rare blood types. Whereas common blood types are expressed in a letter or two, which may be a plus or a minus, a smaller number of people express their blood type in an extensive series of letters in addition to their 'AB-' type designation. The h/h blood group, also known as Oh or the Bombay blood group, is a rare blood type.
Blood group systems
This table was borrowed in significant part from a tabular ISBT document available via the web (columns 1, 2, 3 and 5), with column 4, regarding epitopes and entry notes, being largely unsourced (and therefore suspect material not in compliance with Wikipedia policies). That and other unsourced information—i.e., not appearing in the ISBT table cited, or new to the table since publication of the ISBT table—should be considered as currently unverifiable by this encyclopedia's standards.