Donath-Landsteiner hemolytic anemia due to an anti-Pr-like biphasic hemolysin.

Anemia, hyperbilirubinemia, and reticulocytosis subsequent to viral infection were present in a 32-year-old woman. The direct antiglobulin test was negative, and no unexpected antibodies were detected in pretransfusion tests. Rosettes of red cells (RBCs) around neutrophils were observed in peripheral blood smears, and a Donath-Landsteiner (D-L) test was positive. However, the patient did not show the classic features of paroxysmal cold hemoglobinuria (PCH). There was no hemoglobinuria, and in vivo hemolysis was not precipitated by cold. The D-L antibody was IgG, but classic anti-P specificity was not apparent. Rather, protease- or neuraminidase-treated RBCs, as well as certain sialic acid deficient RBCs of uncommon MN phenotypes, were not hemolyzed in D-L tests. Further, D-L antibody activity could be inhibited by MN sialoglycoprotein. These data support a diagnosis of chronic D-L hemolytic anemia, caused by an anti-Pr-like biphasic hemolysin.