A tissue type test is a blood test that measures substances called antigens on the surface of body cells and tissues. Checking the antigens can tell if donor tissue is safe (compatible) for transplant to another person. This test may also be called HLA typing. Antigens can tell the difference between normal body tissue or foreign tissue (for example, tissue from another person's body). Tissue type helps find the best match for tissues or blood cells (such as platelets). In some cases, a tissue type test may be done to see whether a person has a chance for developing certain diseases that cause the body to attack its own cells, such as autoimmune diseases.

A special pattern of antigens (called tissue type) is present on each person's cells and tissues. Half of each person's antigens come from (inherited) the mother and half from the father. Identical twins have the same pattern, but everyone else has his or her own special pattern. Brothers and sisters have a 1-in-4 chance of having an identical match. Each person's antigen pattern can be "fingerprinted" through a tissue type test.

• The closer the match of antigens, the more likely that transplanted tissues or organs will not be rejected.
• The more similar the antigen patterns are from two people, the more likely it is that they are related.
• Some diseases (such as multiple sclerosis or ankylosing spondylitis) are more common in people who have certain antigen patterns. The reason for this is unknown.

Two main antigen groups are used for a tissue type test. Class I has three classes of antigens (HLA-A, HLA-B, HLA-C) that are found on some kinds of blood cells. Class II has one class of antigens (HLA-D) that are found only on certain cells in the body. There are many different types of antigens in each category.

Why It Is Done

A tissue type test is done to:

• See if the antigen pattern for donated tissue or organs (including a blood platelet transfusion or bone marrow transplant) is a match. The success of a transplant depends on how closely the antigen patterns match. The antigen patterns are most likely to be similar when the donated organ or tissue comes from a close relative of the person.
• See how likely two people are related. If the antigen patterns are very similar, they are likely to be related. But a tissue type can't prove definitively that two people are related. A tissue type test may be done as part of a paternity test to check to see if a man could be the father of a child.
• Find people who may have a high chance of certain autoimmune diseases.

How To Prepare

If you are donating tissue or blood cells, your doctor may want to talk about your medical history-such as a history of cancer, infections, high-risk behaviors, use of drugs, exposure to toxins, and foreign travel. This may be important in understanding whether your donor tissue can be used.