Which diagnostic tests are recommended for confirming Hirschsprung's disease in a child presenting with constipation?

Diagnostic tests recommended for confirming Hirschsprung's disease in a child presenting with constipation include a rectal biopsy when specific clinical features are present. A rectal biopsy should be performed only if the child has any of the following clinical features: delayed passage of meconium (more than 48 hours after birth in term babies), constipation since the first few weeks of life, chronic abdominal distension plus vomiting, a family history of Hirschsprung's disease, or faltering growth in addition to any of the previous features.

Digital rectal examination should be performed only by healthcare professionals competent to interpret features of anatomical abnormalities or Hirschsprung's disease. In children younger than 1 year with idiopathic constipation not responding to optimum treatment within 4 weeks, urgent referral for digital rectal examination is recommended. For children older than 1 year with 'red flag' symptoms suggestive of an underlying disorder, urgent referral to a specialist competent in digital rectal examination and interpretation is advised rather than performing the examination in primary care.

Other tests such as anorectal manometry, plain abdominal radiographs, transit studies, abdominal ultrasound, and gastrointestinal endoscopy are not recommended for diagnosing Hirschsprung's disease.