A 5-yeаr-оld bоy suffering frоm the meаsles complаined of back pain, chills, and stomach pain. A visit to the doctor revealed hemoglobinuria, bilirubinemia, and hemoglobinemia. The child's hemoglobin level had fallen to 6 g/dL. A Donath-Landsteiner test was performed and showed the following: control sample = no hemolysis test sample = hemolysis The results are consistent with what disorder?