At a Glance
Why Get Tested?
When to Get Tested?
Most often, prior to selecting a suitable donor for an organ or bone marrow transplant and for transplant recipients
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?
The Test Sample
What is being tested?
Human Leukocyte Antigens (HLA) are part of the Major Histocompatibility Complex or MHC. They refer to certain specialized proteins (antigens) present on the surface of all nucleated cells in the body and the genes that code for them. Everyone has an inherited combination of HLA antigens present on the surface of his or her white blood cells (leukocytes) and other cells that contain a nucleus. HLA testing identifies the major HLA genes a person has inherited and their corresponding antigens that are present on the surface of their cells.
These antigens and the MHC system play an important role in the management of the immune system. They help 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.
This is important in medicine when transplanting tissue or an organ(s). In bone marrow transplants, the HLA genes in the donor and recipient need to be the same or match as closely as possible for a transplant to be successful and for the tissue not be attacked or rejected by the recipient's immune system. Also, bone marrow donors and recipients must match closely so that the immune cells (lymphocytes) in the donated bone marrow do not attack the recipient's cells in a process called graft-versus-host disease (GVHD; see Common Questions #4).
In solid organ transplants, such as kidney or lung transplants, it is ideal to match the antigens between the donor and recipient; however, the typing incompatibilities are less critical as long as the recipient has not produced 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. When the donor organ is compatible with the intended recipient, it is more likely be recognized as "self" by the recipient and will not be rejected. HLA testing, along with Blood Typing, is used to identify and match organ and tissue transplant donors with recipients who have the same or an acceptable number of matching HLA genes and antigens.
Finding a donor who is compatible with an intended recipient may sometimes be difficult. Part of the reason is because each particular HLA gene can have numerous possible forms or variations (alleles). This is referred to as polymorphic. In addition, there are more than 200 genes that make up the large "gene family" of the HLA system. With many different possible combinations and numerous HLA genes to take into account, it can be a challenge to find a suitable donor. However, HLA genes that are located close together as seen on chromosome 6, are 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 have the same group of HLA genes compared with non-related potential donors. Often, a recipient's parents, children, or siblings may serve as the best transplant matches.
Read the following page of our Universe of Genetic Testing article for more on inheritance and the HLA system.
How is the sample collected for testing?
A blood sample is obtained by inserting a needle into a vein in the arm. Sometimes, for HLA typing, a swab of cells is collected from the inside of the cheek (a buccal swab).
NOTE: If undergoing medical tests makes you or someone you care for anxious, embarrassed, or even difficult to manage, you might consider reading one or more of the following articles: Coping with Test Pain, Discomfort, and Anxiety, Tips on Blood Testing, Tips to Help Children through Their Medical Tests, and Tips to Help the Elderly through Their Medical Tests.
Another article, Follow That Sample, provides a glimpse at the collection and processing of a blood sample and throat culture.
Is any test preparation needed to ensure the quality of the sample?
No test preparation is needed.
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NOTE: This article is based on research that utilizes the sources cited here as well as the collective experience of the Lab Tests Online Editorial Review Board. This article is periodically reviewed by the Editorial Board and may be updated as a result of the review. Any new sources cited will be added to the list and distinguished from the original sources used.
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Delves, P. (Revised 2008 September). Human Leukocyte Antigen (HLA) System. Merck Manual for Healthcare Professionals [On-line information]. Available online at http://www.merck.com/mmpe/sec13/ch163/ch163c.html#sec13-ch163-ch163c-70 through http://www.merck.com. Accessed November 2009.
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(Revised 2009 October). What Is a Blood and Marrow Stem Cell Transplant? National Heart Lung and Blood Institute [On-line information]. Available online at http://www.nhlbi.nih.gov/health/dci/Diseases/bmsct/bmsct_whatis.html through http://www.nhlbi.nih.gov. Accessed November 2009.
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Anne Halpin CHS MSc BSc MLT. Laboratory Scientist, Histocompatibility Laboratory, University of Alberta Hospital.