What investigations should be performed in a neonate with suspected necrotising enterocolitis?

Investigations in Necrotizing Enterocolitis (NEC)

In a neonate with suspected NEC, obtain an abdominal radiograph immediately as the primary diagnostic test, followed by serial films every 6-12 hours, and strongly consider adding abdominal ultrasound to detect bowel wall perfusion, thickness, and free fluid—findings that may identify non-viable bowel before perforation appears on plain films. 1, 2

Initial Laboratory Studies

Complete Blood Count and Inflammatory Markers

• Obtain a complete blood count looking specifically for leukocytosis with left shift or leukopenia (mimicking sepsis), thrombocytopenia (present in 65% of acute cases), and anemia in chronic presentations 1
• Check metabolic panel to identify metabolic acidosis from tissue hypoperfusion and hemodynamic compromise, hypoalbuminemia in chronic cases, and methemoglobinemia from hemodynamic shifts 1

Stool Studies

• Examine stool for blood (gross or occult), mucus, and leukocytes—these are common presenting features of NEC 1
• Blood in stool is a cardinal feature and should prompt immediate radiographic evaluation 1

Radiographic Investigations

Plain Abdominal Radiography (First-Line)

• Pneumatosis intestinalis (gas within the bowel wall) is the pathognomonic finding, seen in 50-60% of cases 1
• Portal venous gas indicates advanced disease and carries a poor prognosis 1, 3
• Pneumoperitoneum (free intraperitoneal air) indicates perforation and is an absolute indication for surgical intervention 1
• Bowel wall thickening >4 mm is abnormal, with thickness >10 mm associated with 60% mortality versus 4.2% for ≤10 mm 1
• Obtain serial radiographs every 6-12 hours during the acute phase to monitor for progression, particularly development of perforation 2, 4

Abdominal Ultrasound (Increasingly Important Adjunct)

Ultrasound provides critical information not available on plain films and should be strongly considered in all suspected NEC cases 1, 2:

• Bowel wall thickening can be precisely measured 1, 2
• Pneumatosis intestinalis detection (often before visible on plain films) 1, 2
• Absent or reduced bowel peristalsis indicates severe disease 1
• Bowel wall perfusion assessment using Doppler—thinning of the bowel wall and lack of perfusion are highly suggestive of non-viable bowel and may be seen before pneumoperitoneum appears on radiographs 2
• Intraabdominal fluid collections that are not visible on plain films 2

The major advantage of ultrasound is earlier detection of severely ischemic or necrotic bowel loops before perforation occurs, which could potentially improve morbidity and mortality since mortality rates are higher after perforation 2

Clinical Assessment Parameters

Cardinal Clinical Features to Document

• Abdominal distention (measure abdominal girth serially) 1
• Feeding intolerance with bilious gastric residuals 1
• Bloody stools (gross or occult) 1
• Systemic signs of sepsis including lethargy, altered mental status, pallor, temperature instability 1, 4

Hemodynamic Monitoring

• Continuous vital sign monitoring for signs of septic shock 4, 5
• Assess perfusion through capillary refill, urine output, and blood pressure 4

Critical Pitfalls to Avoid

• Do not wait for pneumatosis to appear before acting—ultrasound may show non-viable bowel with absent perfusion before radiographic signs develop 2
• Do not rely solely on laboratory values—they are nonspecific and may be normal early in the disease course 1, 4
• Serial imaging is mandatory—a single normal radiograph does not exclude NEC, as the disease can progress rapidly within hours 2, 4
• Plain radiographs have a 92% positive predictive value for intestinal perforation, but ultrasound detects pre-perforation ischemia earlier 3, 2

Monitoring Protocol

Once NEC is suspected, implement the following surveillance:

• Serial abdominal examinations every 4-6 hours 4
• Serial abdominal radiographs every 6-12 hours until clinical improvement 2, 4
• Consider daily ultrasound to assess bowel wall perfusion and detect complications early 2
• Continuous cardiorespiratory monitoring for signs of septic deterioration 4, 5