A 22-year-old female presents with dizziness, fatigue, and jaundice for 2 weeks. Physical examination reveals mild icterus of the sclera and spleen 2 cm below the costal margin. Laboratory tests show hemoglobin (Hb) 65g/L and reticulocytes 0.11 (11%), suggesting hemolysis. Which of the following findings is direct evidence for hemolysis?