Human Leukocyte Antigen Test
The human leukocyte antigen (HLA) test helps detect antigens on the surface of the leukocytes, or white blood cells. It is used to test the compatibility between the tissues of the recipients and donors prior to transplantation.
Principle
Human leukocytes express specific substances on their surface called the HLA antigens. The type of antigens depends on the genetic composition of the individuals DNA. The immune system does not produce antibodies against these antigens as it recognizes them as its own. If the donor tissue used for transplantation contains similar antigens, the immune system will consider it as its own and will not produce antibodies against it. This will increase the chances of a successful transplantation. If the donor and recipient tissues have a very different set of human leukocyte antigens, the recipients immune system will produce antibodies against the transplanted tissue and the body may eventually reject it.
HLA test, also known as HLA typing or tissue typing, is done prior to kidney, bone marrow, pancreas and liver transplantation to check for tissue compatibility. HLA genes and antigens can be grouped into three categories. Class I consists of antigens from HLA-A, HLA-B and HLA-C genes, and are found on all the cells that contain a nucleus. Antigens from HLA-DR, HLA-DQ, and HLA-DP genes are found on B-lymphocytes, activated T-lymphocytes, monocytes, macrophages and dendritic cells and are included in class II. Class III HLA molecules are not tested during tissue typing.
Preparation
Patients do not require any specific preparation before human leukocyte antigen testing. The phlebotomist will draw a blood sample from the arm for the test. Slight bleeding at the blood-drawing site or dizziness may occur. Contact your doctor if the condition does not improve in a couple of hours.
Method
The laboratory may perform serological or DNA tests to detect the compatibility of the tissues. A microcytotoxicity test is performed by mixing the recipients serum with the human leukocyte antigens. The presence of antibodies is detected by clumping of cells. For the crossmatch test, the B- and T-lymphocytes are separated from donors serum. The recipients serum is mixed with both components of the donors serum to detect the presence of matching antibodies and antigens.
Results
The results of HLA test are reported as the percentage of panel reactive antibodies (PRA) and indicate the number of reactive wells during the test. The normal results would be indicated by the identification of HLA-A, HLA-B, HLA-C and HLA-D antigens. Incompatible antigen and antibody combination will indicate unsuccessful transplantation.
The PRA percentage is reported to the United Network for Organ Sharing database, which searches for the compatible donors based on the PRA score.
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