Cross Matching

Cross-matching blood in transfusion medicine, refers to the complex testing that is performed prior to a blood transfusion, to determine if the donor's blood is compatible with the blood of an intended recipient, or to identify matches for organ transplants. Cross-matching is usually performed only after other, less complex tests have not excluded compatibility. Blood compatibility has many aspects, and is determined not only by the bloodtypes (O. A. B. AB), but also by bloodfactors (Rh. Kel, etc.).

Cross-matching is done by a certified laboratorytechnologist, in a laboratory. It can be done electronically, with a computer database, or serologically. Simpler tests may be used to determine blood type (only), or to screen for antibodies (only). (indirect Coombs test).


                                Types of Cross-matching

Electronic cross-matching

Electronic cross-matching is essentially a computer-assisted analysis of the data entered from testing done on the donor unit and blood samples drawn from intended recipient. This includes ABO/Rh typing of the unit and of the recipient, and an antibody screen of the recipient. Electronic cross-matching can only be used if a patient has a negative antibody screen, which means that they do not have any active red blood cell atypical antibodies, or they are below the detectable level of current testing methods. if all of the data entered is compatible, the computer will print a compatibility label stating that the unit is safe to transfuse.

Cross-matching falls into two categories:
Major Cross-match: Recipient serum is tested against donor packed cells to determine if the recipient has preformed antibodies against any antigens on the donor's cells. This is the required cross-match prior to release of a unit of packed cells. -

Minor Cross-match: Recipient red cells are tested against donor serum to detect donor antibodies directed against a patient's antigens. This is no longer required. It is assumed that the small amount of donor serum and antibodies left in a unit of packed cells will be diluted in a recipient.

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