Resolution of ABO Discrepancies

ABO discrepancies are recognized when the reactions obtained in the forward type do not "match" the reactions obtained in the reverse type.  For example,

When a discrepancy is observed one MUST determine if the problem is associated with the forward type, reverse type or both.

FALSE POSITIVE means the reaction should have been NEGATIVE but agglutination occurred. FALSE NEGATIVE means the reactions should have been POSITIVE but no agglutination occurred. The key is to recognize which type of problem is occurring so that appropriate testing can be performed. 

When evaluating an ABO discrepancy it needs to be determined whether there is a problem with the FORWARD type (antigens on cells), the REVERSE type (antibodies in serum/plasma) or BOTH.

Problems With the Forward Type

The forward type detects antigens present on the RED BLOOD CELLS. 

False negative reactions in the forward type may occur due to:

False positive reactions may occur due to:

Problems with the Reverse Type

The reverse type detects antibodies present in the SERUM or PLASMA. 

False negative reactions in the reverse type may be due to weak or missing antibodies due to a variety of factors which influence the production of antibodies. 

False positive reactions may be due to "unexpected antibodies", those antibodies other than anti-A or anti-B.