What are the diagnostic criteria for intussusception in a child presenting with intermittent colicky abdominal pain, vomiting (often bilious) and possible red‑currant‑jelly stool?

Diagnostic Criteria for Intussusception

Intussusception should be diagnosed using ultrasound as the first-line imaging modality, which demonstrates a characteristic "target" or "donut" sign with 98.1% sensitivity and 97.8% specificity, in any child aged 3 months to 5 years presenting with intermittent colicky abdominal pain, particularly when accompanied by vomiting or unexplained lethargy. 1, 2

Clinical Diagnostic Criteria

Classic Presentation (Often Incomplete)

• Intermittent, colicky abdominal pain is the most consistent feature, occurring in 86-100% of cases, manifesting as sudden episodes of intense crying with the infant drawing knees to chest, followed by calm periods between episodes 1, 3
• Vomiting (which may be bilious as obstruction progresses) occurs in the majority but is not the hallmark sign 4, 1
• "Red currant jelly" stools (bloody stools) are time-dependent, typically appearing at a median of 24 hours after symptom onset, and occur in only a subset of cases 5
• Palpable abdominal mass may be present but is inconsistent 6

Critical Clinical Pitfall

The classic triad of abdominal pain, bloody stools, and palpable mass occurs in less than 25% of cases—approximately 86% of infants do NOT present with the complete triad. 3, 7 This makes clinical diagnosis alone unreliable and necessitates imaging confirmation. 8

Additional Presenting Signs

• Unexplained lethargy or altered mental status should prompt immediate evaluation for intussusception, as this may be the predominant presenting feature 1, 3
• Irritability is commonly seen 6
• Rectal examination positive for occult blood is frequently present and should be performed 6

Imaging Diagnostic Criteria

First-Line: Ultrasound (Preferred)

Ultrasound is the diagnostic modality of choice with sensitivity of 97.9-100% and specificity of 97.8-99%. 1, 2, 9 The American College of Radiology recommends ultrasound as first-line imaging to avoid radiation exposure. 7

Diagnostic ultrasound findings:

• Characteristic "target" or "donut" sign on transverse view 1, 2
• "Pseudokidney" sign on longitudinal view 9

Plain Abdominal Radiographs (Limited Role)

Plain radiographs have poor diagnostic accuracy with only 48% sensitivity and 21% specificity and should NOT be relied upon to exclude intussusception. 5, 8 However, they may show: 4, 1

• Dilated small-bowel loops with air-fluid levels
• Paucity of colonic gas
• Soft tissue mass (when present)

Radiographs are primarily useful for detecting complications such as intestinal perforation or obstruction, not for diagnosis. 4, 7

High Specificity Clinical-Radiographic Combination

When a highly suggestive abdominal radiograph is combined with abdominal pain, lethargy, and vomiting, specificity reaches 95% (comparable to ultrasound at 93%), and ultrasound may not be needed before proceeding to enema reduction. 5 However, given the low sensitivity of radiographs alone, this approach should be reserved for cases with unequivocal radiographic findings.

CT Scan (Limited Pediatric Role)

CT provides comprehensive anatomic information and is preferred in adult patients and when evaluating for underlying pathologic lead points, but is not first-line in typical pediatric cases due to radiation exposure. 1, 7

Age-Specific Diagnostic Considerations

• Peak incidence: 5-9 months of age 1, 3
• Uncommon before 3 months of age 4, 3
• 75-90% of cases in typical age range (3 months to 5 years) are idiopathic with no identifiable lead point 1, 3, 7
• 10-25% have identifiable pathologic lead points in the typical age range 1, 3
• Neonates, older children, and adults have lead points in 86-93% of cases, requiring more comprehensive imaging evaluation 1

Diagnostic Algorithm

1. Maintain high clinical suspicion in any child 3 months to 5 years with intermittent abdominal pain, vomiting, or unexplained lethargy 1
2. Perform rectal examination with occult blood testing 6
3. Obtain ultrasound immediately as first-line imaging (do not wait for bloody stools to develop) 1, 7, 2
4. Consider plain radiographs only if perforation or other complications are suspected clinically 4, 7
5. Do NOT withhold pain medication while awaiting diagnosis—this obsolete practice causes unnecessary suffering and impairs examination quality 7

Common Diagnostic Pitfalls to Avoid

• Do not rely on the classic triad—it is present in fewer than 25% of cases 3, 7
• Do not use plain radiographs to exclude intussusception due to low sensitivity (48%) 5, 8
• Do not delay imaging waiting for bloody stools—they appear late (median 24 hours) and are absent in many cases 5
• Do not dismiss the diagnosis in very young infants (<3 months) or older children, though it is less common in these age groups 4, 3