What does blood type mean?

Blood type determines who you can donate blood to and who you can receive it from.
Blood type determines who you can donate blood to and who you can receive it from.

You must have heard about the terms “blood group” or “blood type.” If you ever have undergone surgery or been admitted to a hospital for medical conditions, your doctor might have examined your blood for various parameters, such as blood counts and blood type. Your blood contains various cells and the liquid portion is called the plasma. The red blood cells or RBCs present in the blood carry certain molecules, called antigens, on their surface that determine what blood group you have. The antigens depend on the genes you inherit from your parents. These antigens may be grouped in various categories to form a system for blood typing called the ABO system. Based on this classification, your blood group may be

  • A: This type of blood group means the RBCs have the antigen called antigen A on their surface. Apart from the ABO antigens, there is another important antigen on the RBC surface called the Rh antigen. If a person with blood group A bears Rh antigen on their RBCs, the blood group is called A+ (A positive). Likewise, if the Rh antigen is absent the person will be A- (A negative).
  • B: People with the B antigen on the RBC surface have blood group B. This can also be either blood group B+ or B- based upon the Rh antigen status.
  • O: Blood group O means that both antigen A and B are absent from the RBC surface. Blood group O can be O- (O negative) or O+ (O positive) depending upon the absence or presence of the Rh antigen on the surface of the RBCs.
  • AB: Some people may have both the antigens, A and B, on the surface of the RBCs. When both antigens are present, the blood group is called the AB blood type. This may also be AB- or AB+ depending on the absence or presence of the Rh antigen on the surface of the RBCs.

The table below includes various blood types.

Table 1. Blood Types

A negative (A-)A positive (A+)
B negative (B-)B positive (B+)
AB negative (AB-)AB positive (AB+)
O negative (O-)O positive (O+)

What are the 3 rarest blood types?

The blood types vary depending on the genetic makeup of an individual. Since there are differences in the distribution of genes in different parts of the world, the rarest and most common blood groups also vary in different populations across the globe. The rarest blood type in the United States is the AB- (AB negative) blood type, which is seen in just 0.6 percent of people followed by B- (found in 1.5 percent of the United States population) and AB+ (present in just 3.4 percent of people in the United States).

Table 2. The Various Blood Types and Their Prevalence in the United States

Blood type

Prevalence in the United States (Percentage

of the United States population)

A negative (A-)6.3%
A positive (A+)35.7%
B negative (B-)1.5%
B positive (B+)8.5%
AB negative (AB-)0.6% (Rarest)
AB positive (AB+)3.4%
O negative (O-)6.6%
O positive (O+)37.4%

What is the importance of blood type?

Your blood group varies depending on the tiny molecules called blood group antigens that are present on the surface of your red blood cells or RBCs. The antigens depend on the genes you inherit from your parents. These antigens also determine the presence of certain antibodies against blood group antigens in your blood. Thus, a person with blood group A will not have antibodies against the A antigen in their blood. Similarly, a person with AB type of blood will not have antibodies to both blood group antigens A and B. The presence of the antibodies is responsible for the blood transfusion reactions that occur when incompatible blood is transfused into a person. Your blood group determines the blood type you can receive and who you can donate your blood to.

Table 3. Blood Type Compatibility for Transfusion

Blood typeCan donate blood to people with these blood groupsCan receive blood from people with these blood groups
A negative (A-)A-, A+, AB-, AB+A-, O-
A positive (A+)A+, AB+A+, A-, O+, O-
B negative (B-)B-, B+, AB-, AB+B-, O-
B positive (B+)B+, AB+B+, B-, O+, O-
AB negative (AB-)AB-, AB+AB-, A-, B-, O-
AB positive (AB+)AB+All Blood Types
O negative (O-)All Blood TypesO-
O positive (O+)O+, A+, B+, AB+O+, O-

It has also been observed that people who have certain blood types are prone to certain maladies. It has been observed that people with blood group A are most prone to throw clots and have heart disease. <i>H pylori</i> infection is associated most with people who have O type blood. People with B type blood are most susceptible to TB and <i>E coli</i> infections. These associations are mostly due to a specific subset of the cell proteins present along with the blood group antigens.

SLIDESHOW

Anemia Symptoms and Signs, Types, Treatment and Causes See Slideshow

Health Solutions From Our Sponsors

Medically Reviewed on 11/25/2020
References
Medscape Medical Reference

American Red Cross


Stanford Blood Center


Inova


Wiley Interdisciplinary reviews. Systems Biology and Medicine.