Healthy Living

Different Blood Types and What They Mean

The four main types of blood are A, B, AB and O--each with a negative or positive subtype.

Different Blood Types and What They Mean

The ABO (A, B, AB, or O) blood group system is used to classify different types of antibodies in the plasma and antigens in the red blood cells (RBCs). The ABO blood group and RhD antigen determine the type of blood that is a perfect match for blood transfusions. 

The four ABO blood groups are: 

  • Group A: This blood group has A antigens on the surface of RBCs with B antibodies in the plasma. People who have type A blood can give or donate RBCs to those who have blood type A and AB.
  • Group B: This blood group has B antigens on the surface of RBCs with A antibodies in the plasma. People who have type B blood can give or donate RBCs to people who have blood type B and type AB.
  • Group AB: This blood group has both A and B antigens on the surface of RBCs but neither has A nor B antibodies in the plasma. For this reason, people who have type AB-positive blood are considered as universal plasma donors.
  • Group O: This blood group has neither A nor B antigens on the surface of RBCs but has A and B antibodies in the plasma. The most common blood type is O-positive and those who have O-negative blood are considered as universal donors. This means that their RBCs can be transfused to any type of blood.

Another classification of blood is the Rh factor or RhD antigen. Rh-positive means blood has Rh factor while Rh-negative means without Rh factor. Thus, in the ABO/Rh blood group system, there are eight blood types. 

According to America's Blood Centres, the following is the estimated distribution of people's blood types in the United States:

  • A+ (31%)
  • A- (6%)
  • B+ (9%)
  • B- (2%)
  • AB+ (3%)
  • AB- (1%)
  • O+ (39%)
  • O- (9%)

Compatible Blood Group Types

For safe blood transfusions, blood types must be specifically matched. Moreover, people who are Rh-negative also receive Rh-negative blood but those who are Rh-positive may receive Rh-positive or Rh-negative blood. In most cases, O-negative blood can be safely transfused to anyone because it does not contain A, B, or RhD antigens on the surface of RBCs. This blood type may also be given in medical emergencies, in which a patient's blood type is unknown. It is also compatible with other ABO and Rh blood group systems. 

Blood Group Type

Compatible Blood Type

A+

A+, A-, O+, O-

A-

A- & O-

B+

B+, B-, O+, O-

B-

B- & O-

AB+

AB+, AB-, A+, A-, B+, B-, O+, O-

AB-

AB-, A-, B- & O-

O+

O+ & O-

O-

O-

It is highly recommended for patients to receive blood and plasma that have the same ABO and Rh blood group, but when the required type of blood is unavailable, patients may be transfused with an alternative but compatible blood groups: 

Blood Group Type

Compatible Plasma Type

A

A, AB

B

B, AB

AB

AB

O

O, A, B, AB

ABO Incompatibility 

When a person receives the wrong blood type during a blood transfusion, an ABO incompatibility reaction takes place. Although it's rare, an ABO incompatibility due to wrong blood type transfusion can be a potentially life-threatening event. Doctors are aware of the dangers of wrong blood type transfusions, which is why such transfusion reactions are quite rare. 

When you receive blood antigens that are not present in your own blood, your immune system responds and produces antibodies against them. For example, there would be an ABO incompatibility reaction when blood type B or AB is transfused to a patient who has blood type A since this particular patient produces antibodies against B antigens.  When an ABO incompatibility reaction occurs, the immune system attacks and destroys new blood cells. 

To help reduce the risk of an incompatibility reaction, blood banks and most hospitals have standard protocols, which include:

  • Correct labeling of stored blood samples.
  • Matching information of blood samples and donor identities.
  • Double-checking of the blood type of both donor and recipient, including blood packs before each blood transfusion. 

Pregnancy

A blood group test is usually given in pregnant women. ABO incompatibility is the most common cause of hemolytic disease of the newborn (HDN) and maternal-fetal blood incompatibility. Complications may occur if a mother has Rh-negative blood and her child has inherited Rh-positive blood from the father. In HDN, the mother's antibodies cross the placenta and destroy the red blood cells of the fetus. 

Blood Inheritance

Each parent passes one of two ABO genes to their children. The dominant genes are A and B, while O is the recessive gene. A child will have blood type A if an A gene is paired with an O gene. 

  • If both parents have type AB blood, their child may have A, B, or AB blood types.
  • If parent 1 is AB, and parent 2 is B, their child may have A, B, or AB blood types.
  • If parent 1 is AB, and parent 2 is A, their child may have A, B, or AB blood types.
  • If parent 1 is AB, and parent 2 is O, their child may have an A or B blood type.
  • If parent 1 is B, and parent 2 is also B, their child may have an O or B blood type.
  • If parent 1 is A, and parent 2 is B, their child may have an O, A, B or AB blood types.
  • If parent 1 is A, and parent 2 is also A, their child may have an O or A blood type.
  • If parent 1 is O, and parent 2 is B, their child may have an O or B blood type.
  • If parent 1 is O, and parent 2 is A, their child may have an O or A blood type.
  • If both parents have type O blood, their child may also have type O blood.

Rh Factor

Like the ABO genes, every person also genetically inherits one Rh factor gene from each parent. The dominant gene is the Rh-positive gene when it is paired with the Rh-negative gene. 

   Rh Factor  

    Possible Genotypes   

Rh+

Rh+/Rh+
Rh+/Rh-

Rh-

Rh-/Rh-

 Mother 

 Father 

Child

Rh-

Rh+

Rh+

Rh-

Rh-

Rh-

References

Blood Types: What to Know. (n.d.). https://www.webmd.com/a-to-z-guides/blood-types-what-to-know#1

What is blood? (n.d.). http://www.americasblood.org/about-blood/what-is-blood.aspx 

Blood Type Genetics and Compatibility. (n.d.). https://www.bswhealth.com/patient-tools/blood-center/Pages/blood-type-genetics-and-compatibility.aspx

Understanding Your Blood Type. (n.d.). https://www.redcrossblood.org/donate-blood/how-to-donate/types-of-blood-donations/blood-types.html

ABO Incompatibility Reaction(n.d.). https://www.healthline.com/health/abo-incompatibility

Key Takeaways

  • Each parent passes one of two ABO genes to their children. The dominant genes are A and B, while O is the recessive gene.
  • The ABO (A, B, AB, or O) blood group system is used to classify different types of antibodies in the plasma and antigens in the red blood cells (RBCs).
  • The ABO blood group and Rh factor determine the type of blood that is a perfect match for blood transfusions.