- Prozone phenomenon due to excess unbound antibodies may sometimes lead to failure of detection of ABO incompatibility. . The case series describes immunohematology work up of blood group discrepancies of two blood donors.

- Blood grouping was performed by a fully automated immune hematology analyzer (FAIHA Diagast, Qwalys 3, France) based on the principle of erythrocyte magnetized technology. Further immunohematology workup was done by tube technique (at different temperatures and phases) and column agglutination technique (CAT). Antibody titration was done by tube technique at saline and AHG (anti human globulin) phase.

- Type I blood group discrepancy was detected on initial blood grouping done by an automated analyzer. The discrepancy was resolved by repeat blood grouping by tube technique with a remarkable finding of hemolysis in reverse grouping. The lysis was attributed to high titer antibodies (anti-B titer of 512) with demonstration of prozone phenomenon. However, there was no discrepancy between cell and serum grouping by column agglutination technique (CAT).

- Tube technique is the gold standard method for blood grouping and detects blood group discrepancies optimally. Hemolysis which is taken as a positive result, can be best appreciated by tube technique.