A 12-year-old girl is seen because of 1 week of chest pain. The pain is pleuritic in nature and more severe when she is supine. She also complains of 10 days of fever and 5 days of a productive cough. Two months ago, she experienced right knee pain and swelling, which resolved. Since that time, she has had episodes of otitis media severe enough to require bilateral tympanostomy tube placement. In addition, she has had secondary amenorrhea for the past 2 months and has noted tea-colored urine for the past 2 days. She denies weight loss, night sweats, easy bruising, and joint inflammation. Her family recently moved from Florida to a farming community in southern California.

Physical examination reveals a well-developed girl in no distress. Her weight and height are both at the 95th percentile for age. Vital signs include: temperature of 99.9°F (37.7°C), pulse of 123 beats/min, respiratory rate...

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