How does the doctor know if the diagnosis is hirschsprung’s disease?

Delayed BM in nursry. Normal newborns have a bm (stool/poop) in the first 48 hours. Failure to do so along with distended abdomen and vomiting may indicate hirschsprung's disease in which part of the colon has abnormal nerves. Biopsy of the colon makes the diagnosis. Some babies/children may be diagnosed later in which case the symptoms may be a little different (chronic constipation). A contrast enema helps diagnose.
By tissue exam. Delay in stooling in newborn and constipation in infants and children with poor weight gain raise a suspicion of hirschsprung disease. A positive diagnose is made when no ganglion cells are found on full-thickness biopsy specimen from colon.
Usually enema/biopsy. Usual test for Hirschsprung disease is barium enema. If pattern on enema suspicious for disease, biopsies of rectum and colon performed looking for presence or absence of ganglion cells.Rectal manometry is used by some gastroenterologists. Pressure differences between ganglionic and aganglionic segments.