CPT® Code 81376

HLA Class II typing, low resolution (eg, antigen equivalents); one locus (eg, HLA-DRB1, -DRB3/4/5, -DQB1, -DQA1, -DPB1, or -DPA1), each

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, thereby 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 main classes: Class I and Class II. HLA Class II is particularly important for initiating immune responses and consists 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, DRB1*15 indicates a specific allele within the DRB1 locus. The process of HLA Class II typing at low resolution involves identifying antigen equivalents, which is crucial for various clinical applications, including organ transplantation and disease association studies. Molecular methods for HLA typing typically require cell lysis and protein digestion to extract DNA from nucleated cells, followed by amplification using techniques such as polymerase chain reaction (PCR). One specific method for low resolution typing is PCR sequence specific priming (SSP), which utilizes a panel of primer pairs to amplify groups of alleles. Low resolution testing can be performed using specialized test kits or semi-automatic test systems. It is important to note that CPT® Code 81376 is specifically designated for low resolution testing of a single HLA Class II locus, which may include loci such as DRB1, DRB3/4/5, DQB1, DQA1, DPB1, or DPA1. This code is distinct from others that cover broader testing, such as CPT® Code 81375, which encompasses all five HLA Class II loci, and CPT® Code 81377, which is used for testing a single HLA Class II antigen equivalent.