A 2-year-old Chinese boy was admitted to the hospital after 2 days of pallor and fatigue and 1 day of dark urine. There was no recent history of illness, although his mother reported a 1-week history of intermittent, subjective fevers. There was no history of recent travel, no history of recent trauma, no sick contacts, no pertinent family history, no changes in diet, and no medications. His past medical history was significant for self-limited nosebleeds, which had increased in frequency over the few days before admission.

On examination, the patient was afebrile and tachycardic, with an oxygen saturation of 88% on room air. He was pale and tired-appearing on arrival. He was in no respiratory distress, and there was no hepatosplenomegaly or lymphadenopathy. His skin examination was notable for jaundice, but there were no bruises, petechiae, or rash. He was noted to pass cola-colored urine while in the hospital. His...

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