Blood Types

There are four fundamental blood types: A, B, AB and O. Each types is associated with an RH factor, which is positive or negative. This gives rise to eight blood types: A+, B+, AB+, O+, A-, B-, AB-, O-. In the United States, the distribution of these is as follows:

• O+ = 38%
• A+ = 34%
• B+ = 9%
• O- = 7%
• A- = 6%
• AB+ = 3%
• B- = 2%
• AB- = 1%

There are certain antigenic substances like carbohydrates, proteins, glycolipids and glycoproteins on the surface of red blood cells. The presence of these substances depends on inheritance. The presence or absence of these antigenic substances gives rise to blood type.

Human blood types systems
The International Society of Blood Transfusion acknowledges 29 blood type systems.

1 – ABO blood type system
This is the most significant system in human blood transfusion. The associated anti-A and anti-B antibodies are called as the Immunoglobulin M or IgM antibodies. These are developed during the initial phase of life due to sensitization to environmental substances like viruses, bacteria and food.

2 – Rhesus blood type system
This is the second most significant system in human blood transfusion. RhD antigen is a most significant Rhesus antigen as it is the most immunogenic. RhD negative individuals do not have any anti-RhD IgG or IgM antibodies, but may have IgG anti-RhD antibodies due to a sensitizing occurrence.

3 – Other blood type systems
These are:

• MNS system
• Kell system
• Lewis system

These and other systems have been named according to the patients in whom the antibodies were detected.

Blood transfusion of the Blood types

• O+ can be given to patients with type O+, A+, B+, AB+ and can receive type O+, O-.
• A+ can be given to patients with type A+, AB+ and can receive type O+, A+, O-, A-.
• B+ can be given to patients with type B+, AB+ and can receive type O+, B+, O-, B-.
• AB+ can be given to patients with type AB+ and can receive type O+, A+, B+, AB+, O-, A-, B-, AB-
• O- can be given to patients with type O+, A+, B+, AB+, O-, A-, B-, AB- and can receive type O-
• A- can be given to patients with type A+, AB+, A-, AB- and can receive type O-, A-
• B- can be given to patients with type B+, AB+, B-, AB- and can receive type O-, B-
• AB- can be given to patients with type AB+, AB- and can receive type O-, A-, B-, AB-

Allele
An Allele is a form of genetic information that can be found in the DNA at a particular location and on a particular chromosome. Such co-dominant alleles decide the human blood types. These are of three types:

• IA called as A
• IB called as B
• i called as O

Every individual has a couple of ABO blood type alleles. One is inherited from the biological mother and the other from the biological father. A description of this pair in the offspring's DNA is termed as a "genotype". These genotypes are of six types:

• if one allele is A and other is A, the genotype of the offspring is AA and the blood type of the offspring is A
• if one allele is A and other is B, the genotype of the offspring is AB and the blood type of the offspring is AB
• if one allele is A and other is O, the genotype of the offspring is AO and the blood type of the offspring is A
• if one allele is B and other is B, the genotype of the offspring is BB and the blood type is B
• if one allele is B and other is O, the genotype of the offspring is BO and the blood type is B
• if one allele is O and other is O, the genotype of the offspring is OO and the blood type is O