Table 16. Example of Unexpected Reaction in Forward Typing. | Anti-A | Anti-B | A1 cells | B cells |
| Patient Results | 4+ | 2+ | 0 | 4+ |
Most Probable ABO Type: Group A
Possible Causes: A(B) phenotype, patient cells coated with IgG, acquired B antigen.
Some Strategies for Resolution: Review patient history. 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.
Table 17. Results after Red Blood Cell Testing.| Patient Red Cell | Patient Plasma | Resulting Reaction |
| A antigen (No B antigen) | Anti-B | Negative |
