A 14-year-old girl presents with several weeks of profound fatigue, intermittent low-grade fevers, a facial rash, and joint pain. The rash recently worsened markedly after sun exposure. On physical examination, she has a malar rash extending over the bridge of the nose, but sparing the nasolabial folds, painless oral ulcers, and painful limitation of movement in her wrists and finger joints. On laboratory testing, her WBC is 3,500/mm3, Hgb 9.5 g/dL, platelet count 120,000/mm3. A urinalysis shows 15 to 19 RBC/hpf and an elevated protein of 100 mg/dL. Which of the following tests will most likely be positive? A 4-year-old Caucasian boy presents for evaluation of persistent jaundice. The family reports that the boy had neonatal jaundice on the first day of life, and was treated with phototherapy. He has always had mild icterus, but has had increased icterus at times, especially following other mild illnesses, such as ear infections and colds. There is a family history of his father and paternal grand-mother having undergone splenectomy. On examination, the boy has mild scleral icterus, and his spleen is palpable about 3 cm below the left costal margin. The laboratory evaluation reveals a total bilirubin of 1.9 mg/dL (unconjugated fraction is 1.5 mg/dL), normal liver transaminases, hemoglobin of 11.2 gm/dL, a normal MCV, and an elevated reticulocyte count of 8%. An osmotic fragility test is performed and demonstrates positive results. What is the most likely diagnosis?