A 7-year-old boy was brought to the emergency department with a 2-week history of nausea, vomiting, intermittent left-sided abdominal pain, and left-sided headache. He had recently been feeling tired and very thirsty. He had a history of chronic constipation but no known allergies, fever, or dysuria. His family history included his mother with an astrocytoma and grandmother with Crohn disease. On physical examination, the patient was noted to be fatigued, pale, and tachycardic. His blood pressure was 100/72 mmHg, pulse was 104 beats/min, temperature was 100 °F (37.8 °C), respiratory rate was 18 breaths/min. He appeared euvolemic, although he was later described as dehydrated.