A person’s blood group is determined by the genes they inherit from their parents. It also depends on the kind of antigens on the surface of their red blood cells. Around the world, health practitioners commonly use a combination of the ABO system and the Rhesus factor to classify blood into eight major groups. The classification helps healthcare providers determine a blood sample’s compatibility with other types, which is crucial during donations and transfusions.
The ABO system
There are four major blood types under this system:
- Group A
People with this blood type have A antigens in their red blood cells and anti-B antibodies in their plasma. - Group B
Those with blood group B have B antigens in their red blood cells and anti-A antibodies in their plasma. - Group AB
Individuals with this blood group have no antigens in their red blood cells but both anti-A and anti-B antibodies in their plasma. - Group O
People with this blood group have both A and B antigens but no antibodies.
Rhesus factor
Red blood cells may also have another antigen, a protein named Rhesus:
- RhD Positive
If the Rhesus antigen is present, the blood group is considered RhD positive. - RhD Negative
If the Rhesus antigen is absent, the blood group is considered RhD negative.
When determining one’s blood type for transfusions or other purposes, doctors consider the ABO system and the Rhesus factor.
Blood type compatibility
Before blood is donated, doctors note one’s blood group because they have limited compatibility. Here’s a chart explaining which blood types a person can donate blood to and receive blood from:
- A+
People with this blood type can donate to A+ and AB+ blood groups and receive blood from A+, A-, O+, and O- blood types. - O+
Those with this type can donate to O+, A+, B+, and AB+ blood groups and receive only from O+ and O- types. - B+
Individuals with B+ type can donate to those with B+ and AB+ blood groups and receive blood from B+, B-, O+, and O- types. - AB+
People with this blood type can only donate to others with the same type but receive blood from everyone. - A-
People with this blood type can donate blood to others with A+, A-, AB+, and AB- types but only receive blood from A- and O- types. - O-
O- blood types can donate to everyone but only receive blood from those with O- type. - B-
People with this blood type can give blood to B+, B-, AB+, and AB- blood types and receive blood from B- and O- types. - AB-
Lastly, people with AB- type can give blood to others with AB+ and AB- types and receive from AB-, A-, B-, and O- blood types.
Exceptions in blood compatibility
While there is limited compatibility between most blood groups, there are certain exceptions:
- People with AB blood type can receive any ABO blood type.
- People with O-negative blood type are considered universal donors because their blood does not have A, B, or RhD antigens.
- People with Rh-negative blood can donate to someone with Rh-negative or Rh-positive blood.
Mixing blood against their given compatibility can cause severe complications, such as blood clots, allergic reactions, and even anaphylaxis, which may prove fatal.
