HLA Test

The Human Leukocyte Antigen HLA are proteins or markers that are present on the White blood cells and tissues of the body. HLA test, also known as HLA typing or tissue typing, identifies antigens on the WBCs that determine tissue compatibility for organ transplantation. These HLA markers are inherited from parents. This test is performed for kidney, bone marrow, liver, pancreas, and heart transplants. The transplant will be successful if HLA of donor closely matches with HLA of the patient. If the HLA of the donor and recipient do not match, the immune system of the recipient will assume the donor's HLA antigens as foreign. This causes rejection of the transplanted tissue or organ. This condition is called GVHD or Graft Vs Host disease. Recipients who receive mismatched transplant are at the highest risk of developing this condition. However, GVHD can occur even with proper HLA matching. HLA test also screens recipients for the presence of antibodies that might attack the transplanted tissue or organ as part of an immune response.

Though HLA typing is normally used to screen patients and donors for matching HLA antigens, it can also be undertaken for diagnostic purposes. The presence of HLA antigen B27 is explored to diagnose certain auto immune diseases like ankylosing spondylitis, reactive arthritis and anterior uveitis. HLA-DR15, HLA-DQ6 is associated with Narcolepsy.

Each HLA gene can have huge number of variations called alleles. There are 3 general groups of HLA that play an important role in matching prior to transplantation. They are the A, B and DR antigens. These are inherited from parents, one set of A, B and DR from mother and another set of A, B and DR from father. Thus there are two antigens for each letter and they are identified by different numbers.

HLA Test Process

HLA Test matches alleles of donors and recipients either by performing serological HLA testing or molecular (DNA) typing. Children from the same set of parents are likely to have the best HLA match possible. There is 1 in 4 chances that siblings will inherit the same genes from their parents. This is considered as ideal match.

Once the match has been identified, the next step would be to test for antibodies in the recipient. It is a vital step in HLA testing as antibodies have the potential to attack donor tissues that have the corresponding HLA type.

After testing for antibodies in the recipient, cross matching test is performed to identify donor specific antibodies. Cross matching is performed right before transplant. A cross match determines if the recipient's body contains antibodies formed against the potential donor's antigens. To perform the cross matching, a small amount of the recipient's serum is combined with the donor's white blood cells (T and B lymphocytes). If the recipient has antibodies that are specific to donors HLAs, the donors cells get damaged. This type of reaction is called positive cross match and indicates the incompatibility between recipient and the donor. A blood sample is needed to perform HLA typing. Testing is done using white blood cells and DNA. It takes about two weeks to receive the results.