What is the most appropriate investigation to confirm the source of gastrointestinal bleeding in an infant with hematochezia and anemia?

Radioisotope Imaging (Tc-99m-Labeled RBC Scan) is the Most Appropriate Investigation

In an 11-month-old infant presenting with hematochezia, severe anemia (Hb 70 g/L), and hemodynamic instability (tachycardia 160/min), radioisotope imaging with Tc-99m-labeled RBC scan is the most appropriate initial investigation to confirm the source of bleeding, as it can detect bleeding rates as low as 0.05-0.1 mL/min and is particularly useful for identifying Meckel diverticulum, the most common cause of significant lower GI bleeding in this age group. 1

Clinical Context and Differential Diagnosis

This infant presents with:

• Bright red blood mixed with dark stool suggesting lower GI bleeding with possible upper GI component 2, 3
• Severe anemia (Hb 70 g/L) indicating significant blood loss 2
• Hemodynamic compromise (tachycardia 160/min, elevated BP) requiring urgent localization 1
• Age 11 months making Meckel diverticulum the leading diagnostic consideration 1

Why Radioisotope Imaging is Optimal

Superior Sensitivity for Pediatric Bleeding

• Tc-99m-labeled RBC scans detect bleeding rates as low as 0.05-0.1 mL/min, far more sensitive than CTA (0.3 mL/min) or angiography (0.5 mL/min) 1
• SPECT/CT imaging improves anatomical localization and has reduced the historical localization errors associated with planar imaging 1
• Particularly effective for intermittent bleeding, which is common in pediatric lower GI hemorrhage 1

Age-Appropriate Diagnostic Approach

• Meckel diverticulum is the most common cause of significant lower GI bleeding in infants and young children, and Tc-99m pertechnetate scan (Meckel scan) is the diagnostic test of choice 1
• Abdominal ultrasonography (Option A) would be appropriate for intussusception but does not typically present with this bleeding pattern 1
• Barium studies (Options C and D) are contraindicated in acute GI bleeding as they obscure active hemorrhage and interfere with subsequent endoscopy or angiography 1

Why Other Options Are Less Appropriate

Abdominal Ultrasonography Limitations

• Does not directly visualize bleeding sources or detect active hemorrhage 1
• Useful for structural abnormalities like intussusception but not for confirming bleeding sites 1

CTA Considerations

• Requires IV contrast and radiation exposure, which is less desirable in an infant 1
• Less sensitive than nuclear medicine for low-rate bleeding (0.3 mL/min vs 0.05 mL/min) 1
• May miss intermittent bleeding if not actively hemorrhaging during scan 1

Barium Studies Are Contraindicated

• Barium enema and barium meal have no role in acute GI bleeding evaluation 1
• Positive oral contrast obscures active hemorrhage and prevents subsequent diagnostic procedures 1
• Historical yields of 3-17% for detecting small bowel abnormalities make them obsolete in modern practice 1

Critical Management Considerations

Immediate Stabilization Required

• This infant requires urgent blood transfusion given Hb 70 g/L and tachycardia 2, 3
• Volume resuscitation should occur concurrently with diagnostic workup 4

Diagnostic Algorithm

• Radioisotope imaging should be performed first to localize the bleeding source 1
• If Meckel scan is positive, surgical consultation for resection is indicated 1
• If nuclear medicine is negative or unavailable, consider CTA as second-line in hemodynamically stable patients 1
• Colonoscopy may follow if other studies are non-diagnostic, though challenging in this age group 1, 4

Common Pitfalls to Avoid

• Do not order barium studies in acute bleeding as they render subsequent imaging non-diagnostic 1
• Do not assume upper GI source without investigation despite dark stool component; 10-15% of hematochezia has upper GI origin 5
• Do not delay transfusion while pursuing diagnostic studies in severely anemic patients 2, 3
• Recognize that intermittent bleeding may require repeat imaging if initial study is negative 1