Harr Immunology, Serology & Blood Bank Practice Test 2025 – Comprehensive Exam Prep

A likely reason for a discrepancy in forward blood typing results is the presence of a cold autoantibody. When a patient has a cold autoantibody, it can bind to red blood cells at lower temperatures, leading to false-positive or false-negative reactions during blood typing tests. This situation occurs because traditional blood typing methods often involve testing at room temperature, where cold autoantibodies can cause unexpected agglutination or masking of legitimate antigen-antibody reactions.

In contrast, incorrect reagent usage could also lead to typing discrepancies, but it typically manifests in more systematic or consistent errors rather than sporadic discrepancies. Incompatibility due to previous transfusions would affect crossmatching rather than forward typing, as it involves the patient's immune response to foreign antigens introduced from transfused blood. Sample contamination can lead to erratic results as well, but it's less directly related to the interpretation of forward typing than the interference caused by a cold autoantibody.

Thus, the presence of a cold autoantibody is the most likely cause for discrepancies observed specifically in forward blood typing results.