The currently favored term for the process of confirming a person’s ABO type by checking the antibodies in their serum (or plasma). Other essentially equivalent terms include: “Reverse grouping,” “reverse typing,” “plasma grouping,” and the ever-popular “back-typing.” Serum grouping is the opposite of “cell grouping,” “forward typing,” or “front-typing” (hang in there, we’re pretty much done with the quotation marks!). When blood bankers are determining someone’s ABO type, they are required to do so in two ways. First, they check to see what ABO antigens are present on the person’s red blood cells (this is “cell” or “forward” typing). However, the red cell type must be confirmed by the person’s ABO antibody profile, so we test the patients serum or plasma against both group A and group B red blood cells. The reactions there tell us whether a person has the appropriate antibodies to confirm their red cell type (for example, a person who is blood group A should carry anti-B antibodies). Blood banks are required to perform this test on pretty much every person that they test for ABO type, with two exceptions: 1) When confirming an ABO type on units of labeled red cells that were collected elsewhere, and 2) When doing ABO typing for babies less than 4 months of age.
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