Blood Group Basics


There are eight blood groups and they are classified using two systems.

  • ABO System
  • Rhesus system


ABO System

The first system is called the ABO System and it has four main groups:

  • O Group
  • A Group
  • B Group
  • AB Group


Rhesus System

The second system is called the Rhesus System and is classified as Rhesus Positive (+) and Rhesus Negative (-). The two systems combine to define the following of eight different blood groups of O-, O+, A-, A+, B-, B+, AB- and AB+.

Blood Group Compatibility

The table below demonstrates blood type compatibility. A person with AB+ blood type can receive blood from all of the major blood type groups. At the other extreme people with O- blood type can only receive blood from donors with the same blood type.

Blood Compatability Group


Irish Blood Group Type Frequency Distribution

Blood group O Positive is the most common group in Ireland while AB negative is the least common.

Blood Percentage Group