The 3-day-old full-term neonate has yet to pass meconium and is experiencing significant abdominal distention. The child is otherwise healthy and is not requiring respiratory support. The nurse learns that Hirschsprung disease is suspected and prepares the patient for which test that will definitively diagnose the condition?

The 5-day-old infant presents to the pediatrician's office for a well-baby visit. The parents report being happy that their child is a "good baby" who sleeps a lot and rarely cries. They also report the baby eats 4 times per day, sleeping for 8 hours at night. The nurse notes the baby is at the 70th percentile for weight. Upon assessment, the baby is minimally responsive. The nurse is most concerned about which condition? 

The 68-year-old patient is admitted after 5 days of extremely foul-smelling watery diarrhea with a temperature of 37.9°C, heart rate 118 bpm, and blood pressure 98/52 mmHg. The patient’s recent medical history is significant for being treated 2 weeks ago for a diverticulitis flare-up. Upon assessment, the patient is pale, diaphoretic, and has a tense, distended abdomen that he does not guard with palpation. Lab studies reveal an elevated creatinine (1.9 mg/dL), high white blood cell count (20,000 cells/mL), and normal hemoglobin and hematocrit. The nurse prepares to perform which diagnostic test for this patient?