Investigation of suspected Ael and Bel phenotypes using mixed agglutination reaction with epidermal cells

Background/Aim: ABO discrepancies remain an important challenge in transfusion medicine because discordant forward and reverse grouping results may require additional serological techniques and testing under different temperature and incubation conditions. Accurate investigation of such discrepancies is essential for selection of appropriate transfusion and transplantation strategies. This study aimed to investigate suspected weak A and B phenotypes in two individuals with ABO discrepancies and to assess epidermal mixed agglutination reaction (MAR) as an additional investigational method.Methods: Two individuals with discordant forward and reverse ABO grouping results were investigated using routine and prolonged agglutination testing, adsorption studies, secretor-status determination, epidermal MAR, a lymphocytotoxicity assay and testing for autoimmune acid-reactive warm and cold haemolysins. Prolonged reverse grouping was performed at 4 °C and 37 °C. Adsorption studies were conducted using erythrocytes, leucocytes, saliva or mucosal cells and epidermal cells.Results: In Person A, routine forward grouping showed no agglutination with anti-A or anti-B reagents, whereas reverse grouping demonstrated strong reactivity with A reagent erythrocytes and no reactivity with B reagent erythrocytes. After 1 h of prolonged incubation, the serum agglutinated A erythrocytes at 4 °C (4+) and 37 °C (2+) and B erythrocytes at both 4 °C and 37 °C (3+). Adsorption with anti-A serum reduced agglutination after exposure to the individual's erythrocytes, leucocytes, mucosal cells and epidermal cells. A blood-group substance was detected in saliva and epidermal cells adsorbed anti-A antibodies in MAR. Autoimmune acid-agglutinating antibodies were not detected. The combined serological findings were consistent with a suspected Ael phenotype. In Person K, routine forward grouping showed no agglutination with anti-A or anti-B reagents, while reverse grouping demonstrated reactivity with A erythrocytes but not with B erythrocytes. Following 1 h of prolonged incubation, A erythrocytes were agglutinated at 4 °C and 37 °C (4+ at both temperatures), whereas B erythrocytes were agglutinated at 4 °C (3.5+) and 37 °C (3+). Adsorption with anti-B serum reduced agglutination after exposure to the individual's erythrocytes, leucocytes and epidermal cells. B blood-group substance was detected in saliva and epidermal cells adsorbed anti-B antibodies in MAR. These findings were consistent with a suspected Bel phenotype.Conclusion: These two cases illustrate complex ABO discrepancies that could not be resolved by routine forward and reverse grouping alone. Prolonged incubation, adsorption studies, secretor-status determination and epidermal MAR provided complementary evidence of very weak Aand B-related antigenic activity. The combined findings were consistent with suspected Ael and Bel phenotypes; however, definitive subgroup assignments were not established. Epidermal MAR may represent an additional investigational approach in selected cases of suspected weak ABO phenotypes, but its diagnostic performance and clinical utility require validation in larger studies.