How can I differentiate between functional constipation and constipation due to an underlying medical condition in children?

To differentiate between functional (idiopathic) constipation and constipation caused by an underlying medical condition in children, a thorough history and physical examination are essential.

• History-taking: Look for 'red flag' symptoms that suggest an underlying disorder rather than idiopathic constipation. These include constipation present from birth or the first few weeks of life, delayed passage of meconium (>48 hours in term infants), chronic abdominal distension with vomiting, faltering growth, family history of Hirschsprung's disease, neurological symptoms such as weakness or abnormal reflexes in the lower limbs, and abnormal stool patterns like ribbon stools in infants ²,¹.
• Physical examination: Inspect the perianal area for abnormalities (fistulae, bruising, multiple fissures, abnormal anus position or patency), assess for gross abdominal distension, examine the lumbosacral region for signs of spinal abnormalities (e.g., sacral agenesis, hairy patches, lipomas), and perform a neuromuscular exam of the lower limbs to detect neurological impairment ².
• Absence of red flags and normal findings on history and examination support a diagnosis of functional constipation. In such cases, children are generally well, with normal growth and development, and no neurological deficits ²,¹.
• Amber flags such as poor diet, insufficient fluid intake, or psychosocial factors may warrant specialist referral but do not necessarily indicate an underlying medical condition ¹.
• Digital rectal examination should only be performed by trained clinicians and is indicated urgently if constipation does not respond to treatment in infants under 1 year or if red flags are present, to exclude conditions like Hirschsprung's disease ¹,².

In summary, functional constipation is diagnosed by excluding red flag symptoms and signs through detailed history and examination, while the presence of red flags or abnormal findings necessitates urgent specialist referral to investigate underlying medical causes.