STEMAcademiaAgriculture & FarmingHumanitiesSocial Sciences

The ABO Blood System and the Most Common Blood Type

Updated on June 13, 2016

Before the ABO blood system was discovered, doctors often wondered why some patients died after a blood transfusion while other patients didn't. This left scientists baffled as to what was happening.

Looking back now, the patients who died probably had incompatible donors. Hence, in those days, patients with the most common blood type probably had a lesser change of death due to an incompatible transfusion.

Basics of the ABO Blood System

ABO and Rh Factor

If you have blood type A or type B, it means there is an antigen (proteins that the body recognises) present on the surface of your RBC, denoted as A or B respectively. People with blood type AB have both A and B antigens. People with blood type O have none of these antigens on their RBC.

Rhesus factor is another set of antigen present or absent on RBC. Rhesus-positive (Rh+) people have the Rh factor present while Rhesus-negative (Rh-) do not have the Rh factor. The presence or absence of Rh factor is denoted by a ‘+’ or ‘-’ behind the blood type, e.g. B+ or B-.

O+

Close to 36.4% of the world’s population have blood type O+. If you are blood type O+, then you will produce antibodies against A and B antigens. This is because these two antigens are foreign to your body. A donor blood that contains A and/or B antigen will lead to complications and may even result in death of an O+ recipient. Hence, O+ patients are allowed to receive blood only from type O donors (O+ or O-) given all other pre-transfusion tests have been cleared. Donors with type O+ are allowed to donate to all other Rh+ blood types.

Our blood type is determined by a pair gene that we receive from our parents – an allele from each parent. If you have blood type O (phenotype) this means that you inherited neither the allele for antigen ‘A’ nor that for antigen ‘B’.

ABO Blood Type Inheritance
ABO Blood Type Inheritance | Source

O-

About 4.3% of the world’s population have blood type O-. Similar to O+, individuals with blood type O- will produce antibodies that will attack A and B antigens. These two antigens are foreign to O- people. O- patients are allowed to receive blood only from type O- donors.

Blood type O- can be received by patients of all blood types because they have neither the A nor the B antigens. This is why donors of blood type O are called universal donors.

People who are Rh- have a homozygous genotype (--). Rh- recipients are not allowed to receive Rh+ donor blood because Rh- recipient will slowly produce antibodies (anti-Rh) against Rh+ RBC. And if they are given this Rh+ donor blood again, this will cause severe complications and may even result to death.

Similar to the ABO blood system, Rh factor is inherent from parents. One allele is received from each parent. On like an Rh- person who received only ‘–’ alleles from both parent (--), an Rh+ person received at least one + from a parent (that is either -+ or ++).

Summary of Blood Compatibility
Summary of Blood Compatibility | Source

A+

About 28.3% of the world’s population have blood type A+. If you have blood type A+, then you will produce antibodies that will attack B antigen because this antigen is foreign to your body. Hence, A+ patients are allowed to receive blood from types A and O donors (both Rh+ and Rh-). People with A+ can donate to both A+ and AB+ patients. Individuals with blood type A+ inherited the allele for antigen ‘A’ from one of the parent and did not inherit the ‘B’ allele.

A-

Approximately 3.5% of the world’s population have blood type A-. Similar to A+, individuals with blood type A- will form antibodies against B antigen. Type A- patients are allowed to receive blood only from blood type O and A donors (only Rh-). Blood type A- can be received by patients with blood type A and AB (both Rh- and Rh+).

B+

Around 20.6% of the world’s population have blood type B+. If you have blood type B+, then you will produce antibodies against antigen A because this antigen is foreign to your body. Hence, B+ patients are allowed to receive blood only from types B and O donors (both Rh+ and Rh-). People with B+ can donate to both B+ and AB+ patients. They inherited the allele for antigen ‘B’ from one of the parent and did not inherit the allele for antigen ‘A’.

B-

Close to 1.4% of the world’s population have blood type B-. Just like B+, individuals with blood type B- will form antibodies against antigen A. Patients with blood type B- are allowed to receive blood only from blood type O and B donors (only Rh-). Blood type B- can be received by patients with blood type B and AB (both Rh- and Rh+).

Blood Type AB+

About 5.1% of the world’s population have blood type AB+. If you have blood type AB+, then you have both A and B antigen and will not produce antibodies against them. Therefore, AB+ patients are allowed to receive blood from all donors, of course after satisfactory pre-transfusion screen. For this reason they are referred to as universal recipients. However they can donate blood only to AB+ patients.

If you have blood type AB (phenotype) this means that you inherited the allele for ‘A’ antigen from one parent and that of ‘B’ antigen from the other parent. This is known as a heterozygous trait (genotype).

Both A and B antigens are expressed in AB blood groups this is an example of co-dominance in genetics. This means that both proteins are expressed on RBC rather than one being overridden by another like in the case of other phenotypes like hair color (Mendelian laws of inheritance) where one allele is dominant and another is recessive.

Blood Type AB-

Approximately 0.5% of the world’s population have blood type AB-. Similar to AB+, individuals with blood type AB will not produce antibodies against A and B antigens. Type AB- patients are allowed to receive blood from all other Rh- blood types. On the other hand, blood type AB- can be received only by patients of blood type AB (both Rh+ and Rh-).

Approximate distribution of the ABO blood system to look at the most common blood type
Approximate distribution of the ABO blood system to look at the most common blood type | Source

What are the Most Common Blood Types?

Rh+ blood types are more common than Rh- blood types. The most common blood type in humans is O+ (~36.4%). Next in line are blood types A+, B+ and AB- with percentages approximately 28.3%, 20.6% and 5.1% respectively. The least common blood type is AB- (~0.5%). Other rare blood types are B-, A- and O- with percentages approximately 1.4%, 3.5% and 4.3% respectively.

Comments

    0 of 8192 characters used
    Post Comment

    No comments yet.