Rh "null" is not always null.
D000328:Adult; D000744:Anemia, Hemolytic, Autoimmune / Q000209:etiology; D000888:Antibodies, Anti-Idiotypic; D004912:Erythrocytes / Q000276:immunology; D005260:Female; D006801:Humans; D007519:Isoantigens; D008875:Middle Aged; D012204:Rh-Hr Blood-Group System
D000888:Antibodies, Anti-Idiotypic; D007519:Isoantigens; D012204:Rh-Hr Blood-Group System