CPT® Code 81375

The human leukocyte antigen (HLA) system is a critical component of the major histocompatibility complex (MHC), which plays a vital role in the immune system's ability to recognize self from non-self. This system is essential for the identification of specific characteristics of an individual's cells and tissues, enabling the body to defend against foreign substances, including microorganisms and non-self cells. The HLA system is located on the short arm of chromosome 6 and is divided into two classes: Class I and Class II. HLA Class II is particularly important as it consists of five loci—DR, DQ, DP, DM, and DO—with DR, DQ, and DP being the most significant for immune response. Each locus contains various 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 instance, DRB1*15 indicates a specific allele within the DRB1 locus. HLA Class II antigens are crucial for initiating general immune responses. The process of HLA typing involves extracting DNA from nucleated cells, which requires cell lysis and protein digestion. Most molecular methods for HLA typing utilize polymerase chain reaction (PCR) techniques, specifically PCR sequence specific priming (SSP) for low resolution typing. This method employs a panel of primer pairs to amplify groups of alleles, allowing for the identification of antigen equivalents. The CPT® Code 81375 is used when low resolution testing for all five HLA Class II loci—DRB1, DRB3, DRB4, DRB5, and DQB1—is performed. In contrast, CPT® Code 81376 is designated for low resolution testing of a single HLA Class II locus, while CPT® Code 81377 is used for testing a single HLA Class II antigen equivalent.