Discrepancy in ABO Typing: Possible Patterns

An ABO discrepancy occurs when the front and back type do not agree. The possible paterns can be deduced from the expected results.

Front	Back	Problem Front Type	Problem Back Type
O	A	False negative A antigen	False negative anti-A
O	B	False negative B antigen	False negative anti-B
O	AB	False negative A and B antigens	False negative anti-A and False negative anti-B
A	O	False positive A antigen	False negative anti-A
A	B	False positive A and False negative B ags	False negative anti-B and False positive anti-A
A	AB	False negative B antigen	False negative anti-B
B	O	False positive B antigen	False positive anti-B
B	A	False positive B and False negative A ags	False negative anti-A and False positive anti-B
B	AB	False negative A antigen	False negative anti-A
AB	O	False positive A and False positive B antigens	False positive anti-A and False positive anti-B
AB	A	False positive B antigen	False positive anti-B
AB	B	False positive A antigen	False positive anti-A

where:

• Combinations in bold are unlikely since they involve both a false positive and a false negative.

• Results for anti-A,B are not included.

• Hypogammaglobulinemia could explain absence of all antibodies but would probably not explain the presence of one antibody but not the other.

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