CPT® Code 81377

The HLA Class II typing, low resolution (CPT® Code 81377) is a laboratory procedure that focuses on identifying specific antigen equivalents associated with the human leukocyte antigen (HLA) system. The HLA system is a critical component of the major histocompatibility complex (MHC), which plays a vital role in the immune system by facilitating self-recognition. This means that the MHC helps the body distinguish its own cells and tissues from foreign substances, including pathogens and nonself cells. HLA molecules are located on the short arm of chromosome 6 and are essential for the normal functioning of the immune response. HLA Class II molecules are particularly important as they are involved in initiating immune responses. They consist of five loci: DR, DQ, DP, DM, and DO, with DR, DQ, and DP being the most clinically significant. Each locus can have multiple variants known as alleles, which are designated by the locus name followed by an asterisk (*) and a series of digits that provide specific information about the allele. For example, the designation DRB1*15 indicates a specific allele within the DRB1 locus. The low resolution typing of HLA Class II antigens is performed using various molecular techniques, including polymerase chain reaction (PCR) methods. One such method is PCR sequence specific priming (SSP), which utilizes a set of primer pairs to amplify specific groups of alleles. This low resolution testing is designed to identify antigen equivalents rather than the precise allele sequence. It is important to note that low resolution typing can be conducted using test kits or semi-automatic systems, and it is distinct from higher resolution typing, which provides more detailed genetic information. CPT® Code 81377 specifically applies to the testing of a single HLA Class II antigen equivalent, such as DRB1*15, allowing for targeted analysis of the immune response related to that specific antigen.