Final answer:
The most appropriate next step for a newborn with moderate bilateral hydroureteronephrosis is a thorough assessment by a multidisciplinary medical team, potentially involving tests such as a voiding cystourethrogram to check for vesicoureteral reflux and a urine culture to rule out infection.
Step-by-step explanation:
A 1-day-old male patient with a history of prenatal hydronephrosis and a renal ultrasound (US) showing moderate bilateral hydroureteronephrosis would likely require further investigation to determine the cause and extent of the obstruction or functional impairment. The most appropriate next step would typically involve a multidisciplinary team approach including a pediatric urologist or nephrologist, considering the potential for underlying congenital abnormalities such as congenital obstruction of the urinary tract, duplicated ureter, or vesicoureteral reflux that can compromise kidney function or increase the risk for urinary tract infections (UTI).
In addition to the physical assessment and review of the prenatal and birth history, the next steps might include diagnostic tests like a voiding cystourethrogram (VCUG) to evaluate for vesicoureteral reflux or assessment for other anatomical anomalies. It may also be prudent to culture a urine sample to exclude infection, which can be secondary to the hydronephrosis or an independent cause of the symptoms.