Each of us has several genetic markers located on the surface of most of our white cells. One particular group of genetic markers is called HLA or Human Leukocyte Antigens. These special markers help in determining your “tissue type”. In other words, these help in determining your identity and hence distinguish one person from the other.
The test looks for at least six specific antigens in each donor and recipient. Everyone inherits these HLAs from their parents – one set (including 3 antigens) from the mother and one set (3 antigens) from the father. Hence, you and your parent can have a 3 antigen match, while you and your siblings can have 3 antigen match (25%) or a 6 antigen match (50%). A 6 antigen match is the perfect match and is commonly seen in identical twins. However, it is possible to get a 6 antigen match even with non-related people. The antigens are matched for HLA-A, HLA-B and HLA-DR with HLA-DR compatibility is most important for long term-survival of the transplant.
Hence, each person has a unique set of antigens (i.e. HLA) and tissue typing basically matches HLA of the recipients with that of the donor before kidney transplantation to ensure as close a match as possible. If the antigens do not match well, there is an increased chance of the recipient rejecting the donated kidney i.e. the immune system of the recipient will detect the difference between the two sets of antigens and identify the kidney as a foreign invader and try to damage it. Therefore, the closer two tissues come to matching, the more likely the recipient will accept the donated organ.