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Alternative namesCross matching; Rh typing; ABO blood typing
Blood typing is a test to classify blood by determining the absence or presence of antigens on the red blood cells and the presence or absence of antibodies to these antigens in the serum.
How the test is performed
Adult or child:
How to prepare for the testAdults:
No special preparation is necessary for this test.
Infants and children:
The physical and psychological preparation you can provide for this or any test or procedure depends on your child's age, interests, previous experiences, and level of trust. For specific information regarding how you can prepare your child, see the following topics as they correspond to your child's age:
How the test will feel
When the needle is inserted to draw blood, some people feel moderate pain, while others feel only a prick or stinging sensation. Afterward, there may be some throbbing or a bruise may develop at the site where the needle was inserted. These symptoms are temporary.
Why the test is performed
While the general physical makeup of all people is the same, each individual is unique. Every person has identifiers on cells that allow the body to know that those cells belong to him or her. A and B are common and important identifiers. The O blood type designates the absence of the A and B markers. Another surface identifier, or antigen , on red blood cells is the Rh factor. Whether this antigen is present identifies your blood as Rh+ (positive) or Rh- (negative).
The ABO typing process has two steps: forward and reverse typing. Initially, your blood is mixed with anti-A serum (serum that contains antibodies against type A blood), then with anti-B serum (serum that contains antibodies against type B blood). A determination of the blood type is based on whether or not the blood cells stick together (agglutinate) in the presence of these serums. The blood cells can stick together only when the anti-A antibody binds to the A antigen or the anti-B antibody binds to the B antigen. A laboratory technician can see the cells sticking together when the blood and serum are mixed in a test tube.
The second step involves placing your serum (the liquid portion of the blood without the cells) with blood that is known to be type A and type B (AB). With the results of these two steps, your blood type can be determined accurately.
Rh typing is similar to ABO typing. Here, your blood is mixed with serum containing anti-Rh antibodies and then observed for agglutination. If this occurs, you have Rh-positive blood. If the blood cells do not stick together, you have Rh-negative blood.
Blood typing is especially important during pregnancy. If the mother is found to have Rh-negative blood, then the father should also be tested. If the father has Rh-positive blood, then the mother needs to receive a treatment to help prevent antibodies from forming in the mother's serum. These antibodies can harm a fetus if not treated (see Rh incompatibility ).
Blood typing is also necessary before receiving any blood transfusion.
Note: Notify your health care provider if you have had past transfusion reactions and be sure to tell them about any recent administration of blood products.
What abnormal results meanThere are no abnormal values.
What the risks are
There are many antigens besides the major ones (A, B, and Rh). Many minor antigens are not routinely detected during blood typing. If allowed to go unrecognized, they can initiate a blood transfusion reaction , usually of less magnitude than that of a major blood group incompatibility.
These minor antigens can be detected by cross-matching, which consists of incubating the recipient's serum with the donor's red blood cells (RBCs) in a saline solution followed by the addition of Coombs serum (see Coombs' test - indirect ).
Update Date: 11/7/2002Ezra E. W. Cohen, M.D., Department of Medicine, The University of Chicago, Chicago, IL. Review provided by VeriMed Healthcare Network.
Last updated: Tue, 06 Jan 2009 00:20:03 GMT