Blood Group Conventions

Several conventions exist for designating blood group antigens, genes, phenotypes, and genotypes. Some journals such as Transfusion, the journal of the American Association of Blood Banks (AABB), adhere to the guidelines suggested by Issitt and Crookston. Unfortunately, some journals accept non-standard terminology that can confuse readers. Many technologists also use non-standard terms.

A nomenclature has been devised by the International Society of Blood Transfusion (ISBT). In the ISBT system, which is designed for computerization, each antigen is identified by a six-digit number and alleles are also numbered. For example, in the Kell system the K antigen has the number 006001 (006 is the number given to the Kell system and 001 refers to the K antigen); the K gene is designated Kel 1. Similarly, the k antigen is 006002 and the k gene is Kel 2. This nomenclature is not being used in the routine laboratory at present.

The following guidelines summarize some of the recommendations of Issitt and Crookston. You should adhere to these guidelines when writing about and discussing blood group genetics. They represent accepted usage among professionals.

Antigens and Genes: Genes use italic type or are underlined to distinguish them from antigens. For example, Fy^a or Fy^b indicates the gene, whereas Fy^a indicates the antigen. If a subscript is part of the antigen symbol (e.g., A₁), it becomes a superscript in the italicized gene symbol (e.g., A¹). Note also that the K antigen is not the "Kell antigen," Fy^a is not "Duffy^a," etc.

Phenotypes and Genotypes: A phenotype is a record of the serological reactions observed when red cells are tested with blood group antisera. For example, if cells do not react with anti-Jk^a, they are described as Jk(a-); if they do not react with anti-Jk^a but do react with anti-Jk^b, their phenotype is written Jk(a-b+) and the genotype is Jk^bJk^b. For a system such as MNSs, red cells with the phenotype M+N-S+s- would have the genotype MS/MS; in the Rh BGS, red cells with the phenotype D+C+E-c+e+ would have the most probable genotype CDe/cde or (in shorthand) R¹r.

Allelic Genes and Antithetical Antigens: Genes can have alleles, antigens cannot. Also, genes can have a locus (or loci), antigens cannot. The products of allelic genes, therefore, are referred to as antithetical antigens. Note that red cells cannot be homozygous (or heterozygous); the red cells are from a person who is homozygous for a particular gene. Blood bankers, however, routinely refer to "homozygous cells" where it is assumed that the cells are from a donor who is homozygous for the gene that produces the antigen in question.

Terms to look up

• antithetical

• genotype

• heterozygous

• homozygous

• phenotype

Enrichment activity 3

Visit Review and update: blood group terminology by L.A. Issitt [Immunohematology. Journal of Blood Group Serology and Education 1997;13(1)] Note that, unfortunately, there are a few errors in the online article, e.g., places where genes are not italicized.

Based on the article, answer these questions and e-mail to Pat:

1. When phenotypes are expressed with numbers, such as in the Rh system (in which D=1, C=2, E=3, c=4, and e=5), how should the phenotype Rh: 1, 2, -3, -4, 5 be expressed using DCEce nomenclature?

2. Which of the following uses correct terminology conventions?

   (a) The patient was missing anti B.

   (b) We excluded the antibody using red cells homozygous for the K antigen.

   (c) The maternal anti-D had a titer of 1:512.

   (d) The donor red cells implicated in the delayed hemolytic transfusion reaction were Kidd^a+.

   (e) The patient's genotype was A₁A₂.

Inheritance Patterns

Blood Group Conventions

Quiz #1