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ABO Discrepancy: Example Three

Forward (Cell) Grouping

Reverse (Serum) Grouping

A1 Cells
B Cells

Category: Unexpected reaction in forward grouping.

Most probable ABO type: Group A

Possible Causes: A(B) phenotype, patient cells coated with IgG, acquired B antigen.

Some strategies for resolution: Retype with monoclonal reagents made from another clone or human polyclonal reagents if available; perform an antibody screen to detect autoantibody; perform a direct antiglobulin test (DAT); or wash patient cells and retest.

Testing patient plasma with patient red blood cells
Patients who are truly group A, without any true B antigen, will demonstrate a negative auto control. Since there is no B antigen present on the patient's red cell and there is anti-B in patient plasma, no agglutination should form.

Patient Red CellPatient PlasmaResulting Reaction
A antigen (No B antigen) Anti-B Negative