A COMPARISON OF IN-VITRO TESTS FOR PRE-DIETING THE SEVERITY OF HEMOLYTIC-DISEASE OF THE FETUS AND NEWBORN

Haemolytic disease of the newborn (HDN) is characterized by the presen ce of IgG antibodies in the maternal circulation which cause haemolysi s in the fetus by crossing the placenta and sensitizing red cells for destruction by macrophages in the fetal spleen, Numerous serological, quantitative and cellular assays have been developed to predict the se verity of HDN. These assays all measure and/or characterize alloantibo dies in the maternal circulation. Quantitative assays which accurately measure antibody levels correlate with disease severity better than s erological assays which are inherently less precise. Nevertheless, hig h antibody levels are found in some cases of mild HDN and relatively l ow antibody levels are found in some severe cases. This suggests that disease severity is influenced by factors in addition to antibody conc entration. These factors remain to be fully elucidated but may include the subclass and glycosylation of maternal antibodies, the structure, site density, maturational development and tissue distribution of blo od group antigens, the efficiency of IgG transport to the fetus, the f unctional maturity of the fetal spleen, polymorphisms which affect Fc receptor function, and the presence of HLA-related inhibitory antibodi es. Cellular assays which are sensitive to factors affecting antibody function have therefore been developed in an attempt to improve the pr ediction of disease severity. Although these assays are cumbersome, th ere are now sufficient data to suggest that some cellular assays, when used as part of a structured approach to diagnostic testing, may prov ide clinically-useful information to complement serological and quanti tative assays.