ABO testing is a two-part process, involving testing a person’s red cells for A and/or B antigens as well as testing the person’s serum/plasma for ABO antibodies. Testing the cells is called “cell grouping” (also “forward grouping” or determining someone’s “front type”). In cell grouping, red blood cells are mixed with powerful manufacturer-derived anti-A and anti-B, and evaluated for reaction. Interpretation of the cell group is pretty easy (anti-A+/anti-B– = Group A, etc.), but the result must be correlated with the interpretation of the serum grouping to ensure that both point to the same ABO group. If not, by definition, there is an ABO discrepancy that must be investigated.

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