Clinical Significance of Enzyme Techniques in Irregular Antibody Screening

Background: Enzyme techniques are highly sensitive assays for the detection of weak or developing Rh antibodies. Therefore, many facilities in Japan prefer to use enzyme techniques for irregular antibody screening. However, enzyme techniques often detect cold antibodies and benign autoantibodies. The purpose of this study was to evaluate the clinical significance of enzyme techniques in irregular antibody screening. Methods: Antibodies detected by enzyme techniques (n＝123) were tested by the indirect antiglobulin test (Sal-IAT), polyethylene glycol test (PEG-IAT) and MTS gel system (MTS-IAT). Clinical significance of the antibodies was evaluated according to Ig isotype, level of cell-bound IgG, and monocyte monolayer assay (MMA). Results: Of 123 samples, 71 were positive by all IAT (group A), 34 were positive by PEG-IAT and/or MTS-IAT (group B), and 18 were negative by all IAT (group C). In groups A and B, levels of cell-bound IgG were high and most Ig isotypes were IgG1. In group C, levels of cell-bound IgG were lower and IgM was the main isotype. The MMA-positive rate of group A and B were 87％and 24％, respectively, while that of group C was 0％． Conclusion: PEG or MTS-IAT was able to detect clinically significant antibodies. Most antibodies detected by enzyme techniques alone were clinically non-significant. Enzyme techniques appear to be unnecessary for antibody screening.