What might be the explanation if crossmatch results are negative at the antiglobulin phase and check cells show no agglutination?

When crossmatch results are negative at the antiglobulin phase and check cells show no agglutination, the lack of agglutination can be attributed to the inactivation of the antihuman globulin (AHG) reagent by residual patient serum. In this case, if the serum contains high levels of antibodies, they could interfere with the functioning of the AHG reagent, preventing it from properly binding to any red cells coated with antibodies during the crossmatch. Consequently, this results in a false negative reaction during the antiglobulin phase.

In addition, check cells are used to verify the performance of the AHG phase—if they're not agglutinating when they should, it indicates that there's an issue with the test. If the AHG is inactivated, the check cells would not show agglutination either, confirming that the AHG is not functioning as intended.

By contrast, if red cells were overwashed, this could lead to the removal of antibodies from the test system but shouldn't generally interfere with the AHG itself; similarly, a centrifuge set too high could affect sedimentation but would not influence AHG activity. Finally, while not adding enough check cells could lead to a lack of agglutination