A 6-week-old girl with constipation, fussiness.

This 6-week-old girl was seen in the emergency room due to constipation and increased fussiness. She had tactile fever the night before admission, but her mother hadn’t taken her temperature. She had no bowel movements for the previous 2 days. Normally, she had three to fi ve formed bowel movements each day. She had been eating normally but was fussier over the past several days. In addition, she had several episodes of non-bloody, nonbilious “spitting up.” She was a 6-lb product of a fullterm pregnancy to a 30-year-old gravida 2 para 2 woman. There were no perinatal complications. Family history was unremarkable. She had been taking cow’s milk-based formula well, 3 to 4 oz every 3 to 4 hours. On exam, she was alert and fussy but easily consoled. Her temperature was 38.9°C, but other vital signs were normal. Her weight, length, and head circumference were in the 20th percentile. HEENT exam was unremarkable. Lungs were clear. Cardiac exam was normal. Abdomen was soft and nontender without masses or organomegaly. Genitalia were normal. On admission, her complete blood count, serum chemistries, and urinalysis were normal. Lum-