Forward and reverse ABO typing are both performed in order to validate the ABO interpretation. Blood groups (with the exception of the AB blood group) possess naturally occurring ABO antibodies. These antibodies are present in the plasma when the corresponding antigen is absent from the red cells.
An ABO typing discrepancy occurs when forward and reverse typing reactions do not correlate or when test results are interpreted as unexpected reactions. ABO discrepancies MUST be resolved PRIOR to the administration of blood components. A transfusion reaction could occur if cellular or non-cellular blood components are administered to a patient who demonstrates an ABO discrepancy.
Patient Blood Groups and Corresponding Naturally Occurring Plasma Antibodies
|Blood Group||RBC Antigen||Naturally Occurring Antibody|
| A|| A only|| Anti-B (IgM)|
| B|| B only|| Anti-A (IgM)|
| AB|| A and B|| None|
| O|| None|| Anti-A, B (IgM)|
Discrepant reactions are reactions that result in outcomes that do not fit into the above table.