Discrepancies Information and Courses from MediaLab, Inc.

ABO antibodies are not usually produced by an infant until 3 to 6 months of age. Antibodies found in the sera of newborns are almost always IgG, passively acquired from the mother. Thus, serum testing of newborns is not performed. Anti-A and anti-B titers are highest at ages 5-10 years and then they gradually decrease. Thus, in elderly patients, ABO antibodies may be difficult to detect. In patients with hypogammaglobulinemia, some leukemias, lymphomas or patients who are taking immunosuppressive drugs, the expected antibodies may be weak or even absent, reflecting the low levels of gamma globulin in the patient’s serum. As previously mentioned, these and other ABO typing discrepancies must be resolved before true ABO type can be determined.

The composite image shown on the right illustrates the ABO typing reactions that were obtained for a patient. This particular case illustrates an ABO discrepancy. An ABO discrepancy occurs when the results of forward and reverse typing do not match. The reactions shown are described below in descending order:Patient red cells with reagent anti-A: negative reaction.Patient red cells with reagent anti-B: 4+ agglutination.Patient red cells with reagent anti-D: 4+ agglutination.Patient serum with reagent A1 red cells: negative reaction.Patient serum with reagent B red cells: negative reaction.This patient forward types as a group B, but reverse types as a group AB. (A group B patient should have anti-A. This patient demonstrates neither anti-A nor anti-B, similar to an AB patient). Further workup is necessary to determine the ABO type since the forward and back typing do not match. In this case, incubation at 40 C demonstrated the presence of weakened anti-A. The patient was therefore typed as group B. This case is an example of an ABO discrepancy which was due to a "missing" anti-A antibody. This could be due to old age, severe illness or immunosuppression. Although evaluation of ABO discrepancies is beyond the scope of this course, it is important to note that all ABO discrepancies must be resolved before blood products can be released for transfusion.This patient is Rh (D) positive, as evidenced by the strong agglutination of his cells with reagent anti-D antibody.