CPT® Code 81371

The HLA Class I and II typing, low resolution (CPT® Code 81371) is a laboratory procedure that focuses on identifying specific human leukocyte antigens (HLAs) associated with the immune system. The HLA system is a critical component of the major histocompatibility complex (MHC), which plays a vital role in the body's ability to recognize its own cells and tissues while defending against foreign invaders, such as pathogens and non-self cells. HLAs are located on the short arm of chromosome 6 and are essential for the proper functioning of the immune response. They are categorized into two classes: Class I and Class II. Class I HLAs, which include the most significant loci A, B, and C, are crucial for presenting antigens to immune cells. Class II HLAs consist of five loci—DR, DQ, DP, DM, and DO—with DR, DQ, and DP being the most clinically relevant. Each locus can have multiple variants known as alleles, which are designated by a specific nomenclature that includes the locus name followed by an asterisk and a series of digits indicating the allele group and specific variant. The identification of these alleles is important for various medical applications, including organ transplantation, disease susceptibility assessments, and understanding immune responses to infections and autoimmune conditions. The low resolution typing performed under this code identifies antigen equivalents and is typically conducted using molecular techniques such as polymerase chain reaction (PCR) with sequence-specific priming (SSP). This method amplifies specific groups of alleles, allowing for the verification of HLA types, particularly for HLA-A, HLA-B, and DRB1 loci.