Unexpected Identification of Anti-Diᵃ During Routine Pretransfusion Testing

Anti-Diᵃ is a clinically significant alloantibody directed against a low-prevalence antigen in the Diego blood group system. While rare in most populations, its prevalence is notably higher among East Asian and indigenous South American groups. Detection is often challenging due to the limited presence of Dia (+) cells in routine antibody screening panels.

We describe a case involving a 62-year-old male inpatient at Asia University Hospital who was evaluated for symptomatic anemia. Routine pretransfusion testing using an automated analyzer revealed a positive antibody screen with a sparse and non-congruent reaction pattern. Subsequent manual repeat testing and serologic workup with an 11-cell panel showed reactivity limited to Diᵃ-positive cells. The presence of anti-Diᵃ was confirmed by testing the patient's plasma against Diᵃ-positive red blood cells obtained from the local blood center. After confirming compatibility using the manual polybrene method, the patient received a safe transfusion of leukocyte-reduced red blood cells without adverse reactions.

This case underscores the importance of recognizing atypical reactivity patterns that may indicate a low-incidence antibody. It highlights the need for a rapid pathway to selected cell testing and reference support for accurate antibody identification. While Dia (-) units are readily available, appropriate LIS documentation, clear clinical communication, and staff awareness are essential to ensure safe and timely transfusion care.

This case demonstrates the value of a structured workflow for identifying rare antibodies like anti-Diᵃ and reinforces the need for proactive laboratory protocols to safe and effective transfusion practice.