Evaluation of Anti-A and Anti-B Antibody Titres in Group O Blood Donors Using Saline Agglutination and Indirect Antiglobulin Methods: A Cross-Sectional Study from South India

Background: High-titre anti-A and anti-B antibodies in group O plasma identify “dangerous universaldonors” who may cause passive haemolytic reactions. Saline rapid-spin agglutination mainly detects IgMantibodies, whereas the indirect antiglobulin test (IAT/Coombs’ phase) also detects clinically relevant IgGantibodies. Comparative data from South India are limited.

Methods: This observational cross-sectional laboratory-based study included 106 consecutive eligiblegroup O voluntary blood donors at a tertiary care teaching hospital in Thiruvananthapuram betweenNovember 2017 and November 2019. Serial doubling dilutions of donor serum were tested by salinerapid-spin and by IAT after 37°C LISS incubation with polyspecific anti-human globulin. Haemolysintesting assessed complement-mediated haemolysis using group A and B indicator cells. High titre wasdefined as ≥64. Associations were analysed using chi-squared test (p<0.05 significant).

Results: By saline rapid-spin, high titres were detected in 17.0% of donors for anti-A and 16.0% for anti-B,with an overall dangerous O prevalence of 25.4%. IAT detected higher rates: 25.5% for anti-A and 26.4%for anti-B, with overall dangerous O prevalence increasing to 33.0%, representing about a 50% relativeincrease in detection. A significant association was observed between high saline anti-A titre and highhaemolytic activity (p=0.036; OR=3.00).

Conclusion: IAT detects substantially more high-titre donors than saline agglutination alone, highlightingthe contribution of IgG antibodies. Combined saline and IAT titration with haemolysin testing may improverisk stratification before transfusion of plasma-containing components to non-O recipients.