Unexpected Red Blood Cell Antibodies in Transfusion Recipients: A 10-Year Retrospective Analysis of Prevalence, Specificity, and Clinical Significance

Background Unexpected red blood cell (RBC) antibodies pose significant risks for transfusion safety. Long-term data on antibody prevalence and specificity in Chinese transfusion recipients remain limited. This study aimed to determine the prevalence, specificity distribution, temporal trends, and risk factors of unexpected RBC antibodies at two Chinese secondary hospitals over a 10-year period. Methods This retrospective study included all patients undergoing pre-transfusion antibody screening from January 2014 to December 2023. Antibody detection was performed using the microcolumn gel indirect antiglobulin test. Temporal trends were evaluated by the Cochran–Armitage test. Independent risk factors for alloimmunization were identified using two complementary logistic regression models: a full-cohort model and a female-subgroup model to separately assess the effect of obstetric history. Results Among 44,830 patients, 206 (0.46%) had positive antibody identifications; the alloimmunization rate was 0.39% (176/44,830). A total of 211 alloantibody specificities were identified, with Rh system antibodies predominating (58.3%). Anti-E (26.5%), anti-M (15.6%), and anti-D (11.4%) were the three most common specificities; anti-K accounted for only 0.9%. The annual detection rate increased significantly from 0.28% to 0.57% (P < 0.001). In the full-cohort model, RhD-negative status (aOR = 25.87), prior transfusion (aOR = 2.89), and female sex (aOR = 2.46) were independently associated with alloimmunization. In the female-subgroup model, obstetric history (aOR = 1.72) was an additional independent risk factor. Conclusions The antibody profile was characterized by Rh predominance and near-absence of anti-K, reflecting East Asian antigen frequencies. Prophylactic Rh phenotype matching and inclusion of Mur and Di^a antigens in screening panels are recommended.