Introduction

Introduction

The red cell membrane contains many anchored surface proteins; many of these are polymorphic and carry the different blood groups. Most blood group antigens are glycoproteins and their specificity is mostly determined either by the oligosaccharide or amino acid sequence. 55 human blood group system genes have been identified and sequenced and all the polymorphisms are now known. Most blood group polymorphisms result from single nucleotide polymorphisms (SNPs) encoding amino acid substitutions in either a glycosyltransferase or extracellular domain of a red cell membrane protein.

All authenticated antigens fall into one of four classifications: systems, collections, low and high incidence antigens:

  • Systems consist of one or more antigens controlled at a single gene locus, or by two or more very closely linked homologous genes with little or no observable recombination between them.
  • Collections (200 series) consist of serologically, biochemically, or genetically related antigens, which do not fit the criteria required for system status.
  • 700 Series or low incidence antigens with an incidence of less than 1% and cannot be included in a system or collection.
  • 901 Series or high incidence antigens with an incidence of greater than 90% and cannot be included in a system or collection. 

Terminology in practice

Since their discovery in 1900, a variety of different styles of terminology has been used to denote human blood groups. In 1980 the ISBT established therefore a Working Party to devise and maintain a genetically based numerical terminology for red cell surface antigens. By definition, these antigens must be defined serologically by the use of a specific antibody. All antigens receiving ISBT numbers must have been shown to be inherited characters. The information presented here is an update of one of our publications.

Antigens, phenotypes, and alleles
  • Each antigen belonging to a blood group system is identified by a 6-digit number. The first 3 digits represent the system (e.g. 006 for Kell), the second 3 the specificity (e.g. 006003 for Kpa). Alternatively, the system symbol followed by the antigen number may be used (e.g. KEL003 or, more usually, KEL3 as sinistral zeros may be removed).
  • Phenotypes are represented by the system symbol, followed by a colon, followed by a list of antigens separated by commas. Those antigens shown to be absent are preceded by a minus sign (e.g. KEL:-1,2,3,4). See this table for examples.
  • Alleles are designated by the system symbol, followed by an asterisk, and antigen number, all italicised (e.g. KEL*02). · Genotypes have the system symbol, followed by an asterisk, alleles or haplotypes separated by a slash, all italicised (e.g. KEL*02.03/02). Refer to the allele terminology guidelines and tables for more detail.
  • For collections, antigen, phenotype, gene, and genotype designations are constructed in the same way.
  • For the 700 and 901 series, 700 or 901 replaces the system symbol.
User-friendly and 'everyday' terminology

The numerical terminology was devised primarily for computer storage of information on blood group antigens and to provide a framework for a genetic classification. The numerical terminology is not suitable for everyday communication and many scientists working in the field of human blood groups prefer not to use it in publications. This has led to a variety of alternative names being used for some blood group antigens. In an attempt to introduce some uniformity, a recommended list of alternative names for antigens is provided (see table) (@WP: this table shows phenotype designations, not alternative names for antigens. Therefore, I added this table at the 'phenotype' bullet point above, and it should be removed here. I don't know what table was meant to be here instead). In most cases the name or symbol is identical to that originally published, but in a few cases the more commonly used name is provided. In addition, there are recommended formats for describing phenotypes in the alternative terminology.

Blood Group Allele Terminology

As DNA testing for the prediction of blood group phenotypes has become more widely applied, it is important to have an agreed terminology for the multitude of alleles encoding blood group phenotypes. The below guidelines were approved by the Working Party at the Berlin Congress in 2010. Since the terminology was new and took some time to adopt into routine practice, all comments were discussed in 2012. @WP are these below guidelines still up to date? 

  • General guidelines for 'transfusion medicine' terminology were developed by a group consisting of Geoff Daniels, Marion Reid, Jill Storry, Connie Westhoff, and Martin Olsson.
  • Additionally, special guidelines for naming RH alleles were developed in parallel by Connie Westhoff, due to the complexity of RH.

Any data regarding new alleles should be sent to the blood group assignee (see list of contact persons in 'About' section). @WP add here a sentence about receiving a name for a new allele in that process? 

Glossary

Allele: Alternative forms of a gene that occur at the same chromosomal location and determine specific inherited traits.

Antibody: A protein produced by the immune system that specifically recognizes and binds to antigens, potentially causing adverse reactions in transfusion or pregnancy.

Antigen: A structure on cell surfaces, typically a protein or carbohydrate, that can trigger an immune response and bind to specific antibodies.

Antithetical antigens: Paired antigens that represent alternative forms of the same genetic locus, where individuals typically express one or the other but not both (e.g., M and N antigens in the MNS system).

Blood group: A classification system based on the presence or absence of specific antigens on red blood cell surfaces.

Blood group system: A genetically related group of red cell antigens controlled by a single gene or cluster of closely linked genes.

Blood type: An individual's specific combination of blood group antigens, most commonly referring to ABO and Rh status (e.g., A positive, O negative).

Collections: A category for red cell antigens that are biochemically, serologically, or genetically related and for which the genetic basis has not yet been discovered. Therefore they cannot yet be assigned to a specific blood group system.

Genotype: The genetic makeup of an individual, specifically referring to the alleles present at particular gene locations.

Genotyping/Molecular typing: DNA-based testing methods used to determine blood group genetics and predict antigen expression.

High-prevalence antigen: An antigen present on the red blood cells of most individuals in the general population (typically >90%), making compatible blood difficult to find for those who lack it.

Low-prevalence antigen: An antigen found on the red blood cells of a small percentage of the population (typically <1%), making it relatively rare in the general population.

Null phenotype: The absence of all antigens within a particular blood group system due to genetic deletions or mutations.

Phenotype: The observable characteristics or traits expressed by an individual, determined by their genotype and environmental factors. In the context of blood groups, the phenotype refers to which antigens are detectable on the red blood cell surface through serological testing.

Polymorphism: The occurrence of multiple forms or variants of a gene within a population, leading to genetic diversity.

Rare blood type: Blood lacking high-frequency antigens or possessing unusual combinations of antigens, making compatible donors difficult to find.

Reference sequence: The standard DNA sequence used as a baseline for comparison when identifying genetic variations or mutations.

Series: Specialized antigen categories including low-frequency antigens (700 Series) and high-frequency antigens (901 Series) not yet assigned to blood group systems.

Serological testing: Laboratory methods using antibodies to detect and identify antigens on red blood cell surfaces.

SNP/SNV: Single Nucleotide Polymorphism/Single Nucleotide Variant - a DNA sequence variation where a single nucleotide differs between individuals.

Variant: Any deviation from the reference DNA sequence, including mutations, polymorphisms, and other genetic alterations.

Weak expression: Reduced levels of antigen expression on red blood cells, which may affect serological detection.

 

@WP: any other terms you'd like to add?