Emergencies
As the complete cross-matching process requires approximately 1 hour to be done, it's not always used in emergencies.
In the case of an emergency, a type-specific blood ("uncross-matched blood") can be requested. It is thought that this lifesaving measure is of more benefit than any risk of an antibody-mediated transfusion reaction. This type of blood has less risk of a serious transfusion reaction because it is both ABO-compatible and Rhesus (Rh)-compatible.
Type O and Rh negative blood can be given if the recipient's blood group is not known, as may happen in an emergency.
In an emergency, blood grouping can be done easily and quickly in 2 or 3 minutes in the laboratory on glass slides with appropriate reagents, by trained technical staff. This method depends on the presence or absence of agglutination, which can usually be visualized directly, although occasionally a light microscope may be needed. If laboratory services are not available, another system of deciding which type of blood to use in an emergency is the bedside card method of blood grouping, where a drop of the intended recipients' blood is added to dried reagents on a prepared card. This method may not be as reliable as laboratory methods, which are preferable.
Read more about this topic: Cross-matching
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