Sensitive methods for determining subclasses of IgG anti-A and anti-B in sera of blood-group-O women with a blood-group-A or -B child.

The determination of the subclasses of IgG antibodies against blood groups A and B is important in order to improve our understanding and predict haemolytic disease of the newborn due to IgG anti-A or -B. We describe two techniques that circumvent the problem of the agglutination of A and B red cells by the corresponding IgG antibodies in saline: an antiglobulin consumption test and a modified solid-phase micro-immunofluorescence test. The results of the two techniques are compared with the results obtained in the indirect antiglobulin test beyond the saline agglutination titre in a microplate technique. The solid-phase micro-immunofluorescence test was the most sensitive for the determination of the subclasses of IgG anti-A and -B. Usually sera contained IgG2 anti-A, B in a higher titre than antibodies of other subclasses.