HLA Testing
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- Also Known As:
- Tissue Typing
- Histocompatibility Testing
- HLA Crossmatching
- Formal Name:
- Human Leukocyte Antigen

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At a Glance
Why Get Tested?
Testing is usually performed only in the setting of a planned transplantation where you are either the intended transplant recipient or a possible donor. Testing identifies which human leukocyte antigen (HLA) genes and antigens you have inherited and detects antibodies to HLA antigens that would cause transplants to be unsuccessful; testing may also be done to identify HLA antigen types in platelet blood donors that match transfusion recipients.
When To Get Tested?
Most often, transplant recipients are tested when it is determined that they need a solid organ or hematopoietic stem cell (HSC) transplant. Prior to transplant, potential donors are tested when they are being evaluated for compatibility with a specific recipient or are signing up with a national donor registry.
Some recipients requiring platelet transfusions do not display a rise in their platelet count because of the presence of HLA antibodies. To improve the platelet response, blood donors of platelets are HLA-antigen-matched to the recipient.
Sample Required?
A blood sample drawn from a vein in your arm; sometimes, for HLA typing, a swab from the inside of the cheek (buccal swab)
Test Preparation Needed?
None
What is being tested?
Human leukocyte antigens (HLA) are specialized proteins present on the surface of all cells in the body except red blood cells. The HLA genes that individuals inherit are responsible for the HLA antigens present on their cells. HLA testing identifies the major HLA antigens that are present on the surface of an individual’s cells and the antibodies to HLA antigens as well as the genes that are responsible for HLA antigens, primarily to match transplant donors and recipients.
In humans, the HLA genes are located in region of chromosome 6 called the major histocompatibility complex (MHC). The MHC plays an essential role in the management of the immune system. It helps the body’s immune system distinguish which cells are “self” and which are “foreign” or “non-self.” Any cells that are recognized as “non-self” can trigger an immune response, including the production of antibodies. HLA antibody testing is performed on transplant recipients to determine if they have antibodies that would target the HLA antigens on the donated organ or tissue. HLA antibody testing is also performed on platelet transfusion recipients to determine if they have any antibodies that would target the donor’s platelets and prevent a good response to the transfusion.
For hematopoietic stem cell (HSC) transplant, the HLA genes of the donor and recipient must be the same or match as closely as possible for transplantation to be successful and to lessen the chance of developing graft-versus-host disease (GVHD).
In solid organ transplants, such as kidney, heart, or lung transplants, ABO blood group compatibility is critical. After matching ABO types, it is also beneficial to match the HLA antigens between the donor and recipient. Unlike ABO matching, HLA typing mismatches are less critical as long as the recipient has not developed HLA antibodies directed against donor’s antigens. Various drugs may be administered to help suppress the recipient’s immune system in order to minimize organ rejection.
Finding a donor who is compatible with an intended recipient may sometimes be difficult. Part of the reason is because each HLA gene can have numerous possible forms or variations (alleles). This characteristic is referred to as polymorphic. In addition, there are more than 200 genes that make up the large HLA gene family located on chromosome 6. Considering the many different possible combinations and numerous types of HLA alleles, it can be a challenge to find a suitable donor, especially if the recipient has pre-formed HLA antibodies.
Nevertheless, HLA genes are located close together and inherited together as groups known as haplotypes; thus, a child inherits one haplotype from each parent. Because of this, there is a greater chance that family members will have the same group of HLA alleles compared to non-related potential donors. Often, a recipient’s parents, children, or siblings may serve as the best transplant matches.
Common Questions
View Sources
Sources Used in Current Review
2017 review performed by Wyenona Hicks, MS, MT(ASCP)SBB, Dean R. Sylvaria, BS, CHS Supervisor, Histocompatibility Lab Beth Israel Deaconess Medical Center and the Testing.com Editorial Review Board.
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Smith, S. (2002 June 17). Immunologic Aspects of Organ Transplantation. Medscape from Organ Transplantation: Concepts, Issues, Practice, and Outcomes [On-line information]. Available online at http://www.medscape.com/viewarticle/436533_print. Accessed November 2009.
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