Hemolytic disease of the newborn due to anti-U

Anti-U is a rare red blood cell alloantibody that has been found exclusively in blacks. It can cause hemolytic disease of the newborn and hemolytic transfusion reactions. We describe the case of a female newborn presenting a strongly positive direct antiglobulin test due to an IgG antibody in cord blood. Anti-U was recovered from cord blood using acid eluate technique. Her mother presented positive screening of antibodies with anti-U identified at delivery. It was of IgG1 and IgG3 subclasses and showed a titer of 32. Monocyte monolayer assay showed moderate interaction of Fc receptors with maternal serum with a positive result (3.1%). The newborn was treated only with 48 hours of phototherapy for mild hemolytic disease. She recovered well and was discharged on the 4th day of life. We conclude that whenever an antibody against a high frequency erythrocyte antigen is identified in brown and black pregnant women, anti-U must be investigated.