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Table 3: Testing the Serum with Known Red Cells (Reverse Typing)

Antibodies occur predictably in the sera of all normal adults in association with the ABO antigens. Demonstration of these antibodies is necessary for definitive classification of an individual's ABO cell type. The individual's serum is therefore tested against reagent red cells containing known antigens.

Patient ABO Blood Group

Patient Serum Tested with Known Reagent Cells

A Cells

B Cells

A

0

3-4+

B

3-4+

0

O

3-4+

3-4+

AB

0

0

+ = agglutination (graded 1+ to 4+)
0 = no agglutination or hemolysis