16.3 Terminology and nomenclature - HLA typing and HLA serology

All HLA assignments, irrespective of the method, must comply with the latest report of the WHO Nomenclature Committee for Factors of the HLA System [Marsh, 2010].

HLA typing is now performed by DNA molecular analysis.

HLA typing by DNA-based techniques employs either sequencing or DNA-based probes/primers to type for the presence or absence of sequence motifs. Kits using this technology are able to define the HLA alleles present in an individual to a variable level of resolution dependent on a number of factors. These include the number of probes or primers employed, the number of alleles defined for a given locus, and the HLA alleles present in the individual. Although it is possible to achieve a high resolution or allele level typing using molecular methods, it is not a clinical requirement in transfusion practice.

Each serologically defined HLA antigenic specificity may be encoded by a number of different HLA alleles. Conversely, many HLA alleles have no determined serologically defined antigen. Thus it is not always possible to assign a serological equivalent to each HLA allele [Holdsworth, 2009].

HLA typing results must conform to the recommendations of the WHO Nomenclature committee. Examples of suitable reporting formats as referenced in EFI Standards v.8.0 include the following:

Single alleles

HLA-B*07

Single antigens

HLA-B7

DNA assignment

HLA-A*02,*30; B*07,*44; C*07,*16; DRB1*01,*04; DQB1*05, *03:01

Serological assignment

HLA-A2,30; B7,44; Cw7; DR1,4; DQ5,7

If an HLA typing is performed using DNA methods, it is acceptable to report an HLA serological assignment if required for the purposes of, for example, HLA-matched platelet allocation. The translation of alleles to serological equivalence must be performed according to a documented protocol.

Caution should be exercised if an HLA type assigned using DNA-based molecular techniques is converted into a serological equivalent, and such conversion must always be avoided with alleles for which the phenotype has not been unequivocally defined.

References

Holdsworth R et al. (2009). The HLA dictionary 2008: a summary of HLA-A, -B, -C, -DRB1/3/4/5, and -DQB1 alleles and their association with serologically defined HLA-A, -B, -C, -DR, and -DQ antigens. Tissue Antigens, 73, 95–170. https://doi.org/10.1111/j.1399-0039.2008.01183.x

Marsh SGE (2010). Nomenclature for Factors of the HLA System. Tissue Antigens, 65, 291–455. https://doi.org/10.1111/tan.15495