Serological and Clinical Evaluation of Incompatible Crossmatches Encountered in Pre-transfusion Testing

Background Pre-transfusion testing is essential for preventing incompatible red cell transfusions and associated adverse reactions. Despite modern serological advancements, unexpected alloantibodies, autoantibodies, and monoclonal antibody interference continue to contribute to incompatible crossmatches. This study evaluates the serological patterns, clinical associations, and diagnostic considerations of incompatible crossmatches encountered in routine transfusion practice. Methods This cross-sectional study was conducted at a tertiary-care transfusion service of Swami Rama Himalayan University, Dehradun, India, over a duration of 18 months, from April 2023 to September 2024. Of 34,631 packed red blood cell (PRBC) crossmatches performed, 46 (0.13%) showing major incompatibility were included. Detailed clinical history, hematological parameters, and immunohematological testing, including Direct Coombs Test (DCT), Indirect Coombs Test (ICT), extended antibody panels, and daratumumab interference assessment, were performed. Associations between antibody category and clinical variables were analyzed using Chi-square/Fisher's exact tests, with p < 0.05 considered significant. Results Among 46 incompatible crossmatches, alloantibodies were the most frequent antibody type (24; 52.1%), followed by autoantibodies (16; 34.8%) and daratumumab interference (6; 13.0%). DCT status showed a significant association with antibody type (p = 0.001), with autoantibodies observed exclusively in DCT-positive cases (16/16; 100%), while daratumumab interference occurred only in DCT-negative cases (6/6; 100%). Significant associations were observed for age group (p = 0.012), clinical diagnosis (p = 0.001), previous transfusion history (p = 0.001), number of PRBC units transfused (p = 0.001), hepatomegaly (p = 0.009), and splenomegaly (p = 0.001). Younger patients predominantly exhibited alloantibodies, whereas patients older than 50 years showed contributions from all antibody categories. Autoantibodies predominated in benign hematological disorders (12; 75.0%), while daratumumab interference was confined to hematological malignancies (6; 100%). Gender (p = 0.463) and Rh typing (p = 0.076) were not significantly associated with antibody distribution. Logistic regression analysis did not identify reliable independent predictors due to wide confidence intervals and model instability. Conclusion Most incompatible crossmatches were caused by alloantibodies, though clinically significant contributions from autoantibodies and daratumumab interference were also observed. Strong associations with demographic and diagnostic variables highlight the importance of individualized immunohematological assessment. Routine use of structured diagnostic algorithms can enhance resolution of incompatible crossmatches and strengthen transfusion safety.