Review Question - QID 107985

A 5-year-old African-American male with no previous medical history is taken to the ED by his mother because his urine was darker than normal. She notes that, for the past week, he has had a cough, runny nose, and fever. A few days ago, she gave him a small dose of acetaminophen, which seemed to help. This morning, he complained of worsening fatigue and back pain. When he went to the bathroom, his urine was the color of tea, prompting his mother to bring him to the hospital. In the ED, his vitals are as follows: temperature is 101.6 deg F (38.7 deg C), blood pressure is 120/80 mmHg, pulse is 99/min, respirations are 15/min. His exam is noteworthy for mild scleral icterus and mild splenomegaly. His labs are consistent with acute hemolytic anemia. Peripheral smear is shown in Figure A. What is the underlying cause of the patient's anemia?