G6PD and cold agglutinin disease: In the differential diagnosis an acute onset is more frequently observed in RBC enzymopathies involving the pentose phosphate (PP) shunt (e.g., glucose-6-phosphate-dehydrogenase, G6PD deficit) and in autoimmune hemolytic forms involving complement activation (AIHA caused by warm IgM, warm IgG + C, mixed, and CAD with thermal range close to physiological temperatures) and in paroxysmal nocturnal hemoglobinuria (PNH).