Monocyte monolayer assay as a tool in the early assessment of the severity of the alloantibodies in patients with hemolytic disease of the fetus and newborn

Introduction: Hemolytic disease of the fetus and newborn (HDFN), caused by the transplacental passage of maternal alloantibodies, can lead to progressive fetal organ failure and death from hydrops fetalis. Because serological tests often have limitations in predicting the clinical severity of these antibodies, in vitro assays have become promising tools, allowing the evaluation of the IgG-mediated extravascular hemolysis mechanism via macrophage Fc receptors. We aim to evaluate the monocyte monolayer assay (MMA), considered the most clinically validated tool for predicting in vivo survival in incompatible transfusion situations, as an early predictor of the severity of HDFN in sensitized pregnant women. Methods: A retrospective cohort study was conducted in sensitized pregnant women at the Hospital Italiano in Buenos Aires. The MMA was performed on all patients, dividing reactivity into four groups, G1: MMA >20%, G2: MMA between 10–20%, G3: MMA between 5–10%, and G4: MMA <5% and the results were correlated with the degree of fetal involvement. Results: Thirty-one patients with an MMA index >20% had a significantly higher rate of serious complications, including a 100% need for intrauterine transfusion (IUT). This group also experienced six fetal deaths. In contrast, the 29 patients with an MMA index <20%, including groups 2–4, did not require IUT or postnatal transfusions. Conclusion: MMA results showed a strong correlation with the degree of fetal involvement and may be an early, highly sensitive and specific predictor of the hemolytic potential of maternal alloantibodies.