Abstract

Background: Alloantibodies are immune responses produced by exposure to foreign red blood cell antigens. However, sensitized alloantibodies can lead to hemolytic transfusion reactions and complicate cross-matching procedures. Objectives: This review article aims to demonstrate the prevalence of unexpected alloantibodies across Thailand’s four major geographical regions. Materials and methods: A comprehensive literature search was conducted across PubMed, Google Scholar, and ThaiJo databases using keywords related to unexpected alloantibodies in Thailand, yielding 17 articles categorized by geographical region. Studies were filtered using strict criteria (published 2013-2025, sample size > 100, reporting > 2 alloantibody types) for final data analysis. Results: It is revealed that anti-Mi^a is the highest unexpected alloantibody, with a prevalence rate of 25.9-37.2% across all four regions, followed by anti-E (15.6-20.7%), anti-Le^a (4.7-14.6%), and anti-Le^b (4.6-8.0%), respectively. Interestingly, anti-P1 is remarkably increased in the Northern region (15.1%), whereas anti-Jk^a (4.7%) and anti-Jk^b (2.5%) are specifically higher in the Northeastern region. Conclusion: This review highlights the importance of practicing antibody screening protocols, choosing compatible antigen status, and establishing rare donor registries in Thailand to avoid unexpected alloimmunization, thereby ensuring optimal transfusion safety.