Human blood group systems

346 red blood cell antigens and 33 platelet antigens have been serologically defined.^[1] The genetic basis for most of these antigens lie in 45 red blood cell or six platelet genes. Thirty-five major human blood group systems (including the ABO and Rh- systems) were recognised by the International Society of Blood Transfusion (ISBT) in October 2012.^[2] In addition to the ABO antigens and Rh (Rhesus) antigens, many other antigens are expressed on the red blood cell surface membrane. For example, an individual can be AB RhD positive, and at the same time M and N positive (MNS system), K positive (Kell system), and Le^a or Le^b positive (Lewis system). Many of the blood group systems were named after the patients in whom the corresponding antibodies were initially encountered.

The ISBT definition of a blood group system is where one or more 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".^[3]

Blood grouping postulates

Blood is composed of cells suspended in a liquid-like substance 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

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:

• 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)

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:^[4]

• A1 Negative (A1 −ve)
• A1 Positive (A1 +ve)
• A1B Negative (A1B −ve)
• A1B Positive (A1B +ve)
• A2 Negative (A2 −ve)
• A2 Positive (A2 +ve)
• A2B Negative (A2B −ve)
• A2B Positive (A2B +ve)
• B Negative (B −ve)
• B Positive (B +ve)
• B1 Positive (B1 +ve)
• O Negative (O −ve)
• O Positive (O+ve)

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. This blood phenotype was first discovered in Bombay, now known as Mumbai, in India, by Dr. Y. M. Bhende in 1952.

Blood group systems

References

External links

• ISBT Table of blood group antigens within systems Updated August 2008.
• BGMUT Blood Group Antigen Gene Mutation Database at NCBI, NIH.
• Blood Groups and Red Cell Antigens National Center for Biotechnology Information (NCBI).
• Distribution of Blood Types, Behavioral Sciences Department, Palomar College.
• Blood group antigen proteins