Serum Grouping

Serum grouping is one of the two required phases in determining the ABO type of an adult before transfusion. It is the currently favored term (at least, according to the AABB Technical Manual) for the process of confirming a person’s ABO type by checking the antibodies in their serum (or plasma). Most blood bankers use the term “Reverse grouping” interchangeably (in fact, we may use reverse grouping more often!). In addition, you will often hear lab scientists working in blood banking calling this phase of ABO testing “back-typing.” Serum grouping is the opposite of “red cell grouping,” “forward typing,” or “front-typing” (hang in there, we’re pretty much done with the quotation marks!).

When laboratories 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 “red cell” or “forward” grouping). However, the red cell type must be confirmed by the person’s ABO antibody reactions, so we test the patient’s serum or plasma against reagent (known) group A and group B red blood cells. The reactions tell us whether a person has the appropriate antibodies to confirm their red cell type (for example, a person who appears to be blood group A on red cell grouping should carry anti-B antibodies and not anti-A antibodies).

Blood banks are required to perform serum grouping 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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