How New Blood Group Systems are Recognised and Classified

In general, the majority of the population has one of the ABO blood groups and is Rh positive or negative.

The International Society of Blood Transfusion (ISBT) Working Party for Red Cell Immunogenetics and Blood Group Terminology (ISBT WP) maintains an official record of all currently recognised blood group systems. There are currently 43 recognised blood group systems containing 345 red cell antigens (June 2021). The 43 systems are genetically determined by 48 genes.

How do we find new blood group antigens or systems?

New blood groups are determined by techniques such as proteomics, single nucleoside polymorphism (SNP) arrays, exome sequencing, reactivity in various media, reactivity with null cells, biochemistry, family studies and gene sequencing.

Blood group systems named by the ISBT are as follows.

When the WCBS Immunohaematology Laboratory classifies an antibody as ‘unidentified’, the antibody is generally less common or newly recognised so not included in commercial antibody reagent panels used.

WCBS contributed to the discovery of Rh CEWA (originally named Rh51), an antigen in the Rh system.  Many tests including a family study and DNA tests were performed. Samples were then sent for confirmation testing to the International Blood Group Reference Lab and classified by the ISBT.

For more information, please feel free to visit the ISBT: Red Cell Immunogenetics and Blood Group Terminology ( or contact Ruwayda Soeker, Manager – Immunohaematology (


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