LAUSR

A 2-month-old male, born at 41 weeks via spontaneous vaginal delivery with a birth weight of 3990 g (75th percentile), presented to the emergency department (ED) with poor weight gain. His mother received routine prenatal care, but smoked during the pregnancy. His postnatal course was complicated by hyperbilirubinemia requiring phototherapy. At time of discharge from the nursery, his total bilirubin was below the threshold for phototherapy. His discharge weight was 3796 g down 4.8% from birthweight. At his 2-week follow-up visit, he remained below birth weight. His newborn screen was normal, but he was admitted to an outside hospital for dehydration and poor weight gain. Laboratory results from workup of poor weight gain included hypernatremia of 152 mEq/L (152 mmol/L; normal range = 135-145 mEq/L). During that admission, his formula was changed from 19 calories/ounce to 22 calories/ounce with resultant appropriate weight gain. Discharge weight was not available from his hospital discharge summary, but his sodium level remained elevated at 149 mEq/L (149 mmol/L; normal range = 135-145 mEq/L). Available records did not indicate any follow-up to address the persistent hypernatremia. His weight was recorded as 4252 g at his 1-month follow-up visit, indicating suboptimal weight gain of 9 g/day since birth. His parents were advised to present to the nearest ED for further workup. In the ED, his mother reported his feeds as approximately 120 mL of 22 calories/ounce formula every 2 to 3 hours, with a description of appropriate formula preparation. In addition, she reported occasional emesis and loose stools, which improved after changing to a soybased formula in the previous week. Stools at that time were described as non-bloody and watery. She also reported that he had approximately 10 wet diapers per day, but had no other concerns. Admission examination revealed an afebrile infant with other vital signs within normal limits for age, weight of 4555 g (10th percentile), head circumference 38 cm (23rd percentile), and length 56 cm (20th percentile). He appeared malnourished, jaundiced, and had bilateral eye discharge without conjunctival injection. Abdominal examination was benign, without any palpable masses or hepatosplenomegaly. Genitourinary examination revealed normal external male genitalia and bilateral descended testes. The rest of his examination was unremarkable. Laboratory values were significant for hypernatremia 152 mEq/L (152 mmol/L; normal range = 135-145), mild hyperkalemia 5.5 mEq/L (5.5 mmol/L; normal range = 3.5-5.3), hyperchloremia 112 mEq/L (112 mmol/L; normal range = 98-107), and hyperbilirubinemia, with total bilirubin and direct bilirubin measuring 3.9 mg/dL (66.6 μmol/L; normal range = 0.0-20.5) and 2.4 mg/dL (41.0 μmol/L; normal range = 0.0-5.1), respectively. Bicarbonate was normal at 26 mmol/L (normal range = 22-29), blood urea nitrogen and creatinine were 17 mg/dL (6.1 mmol/L; normal range = 2.18.2) and 0.31 mg/dL (27.4 mmol/L; normal range = 17.7-35.4), respectively. Liver panel showed elevated alkaline phosphatase of 627 U/L (normal range = 122469), aspartate aminotransferase of 55 U/L (normal range = 0-40), and γ-glutamyl transferase of 66 U/L (normal range = 8-61). Urine specific gravity was 1.009 (normal range = 1.005-1.030) and remainder of urinalysis was unremarkable. Urine osmolality and serum osmolality were 157 mOsm/kg (157 mmol/kg; normal range = 100-1000) and 320 mOsm/kg (320 mmol/kg; normal range = 275-295), respectively. Complete blood count was normal. The patient was admitted for further evaluation of poor weight gain (Figure 1) in the setting of multiple abnormal laboratory results.