Which of the following can lead to a discrepancy in blood typing results?

Discrepancies in blood typing results often occur due to various factors that can affect the interpretation of blood antigen-antibody reactions. The factor identified as the antigen masking effect pertains to instances where the presence of certain antigens may be obscured or hidden, preventing accurate identification of blood type. This can occur due to various conditions, such as the presence of soluble antigens or certain blood group antibodies that interfere with the antigenic determinants.

Subgroups of A and B refer to the existence of different variants within the A and B blood groups. These subgroups may have slight structural variations in the antigens that can sometimes cause them to behave unexpectedly during testing, leading to potential misclassification of the blood type. This can happen when a blood sample contains weak subgroups that do not react consistently with standard typing reagents.

Both the antigen masking effect and the existence of subgroups contribute to possible discrepancies in blood typing results. Therefore, acknowledging both factors is essential in understanding how inconsistencies can arise in blood group determination, making the combined choice the correct answer.