What is the most likely investigation to confirm the source of lower gastrointestinal bleeding in an anemic child with normal coagulation tests and passing bright red blood mixed with stool?

Radioisotope Imaging (Meckel's Scan) is Most Likely to Confirm the Source

In an 11-month-old infant presenting with bright red blood mixed with dark stool, anemia (Hb 70 g/L), tachycardia, and normal coagulation studies, radioisotope imaging (Meckel's scan) is the most appropriate investigation to confirm the source of bleeding, as Meckel's diverticulum is the most common cause of significant lower GI bleeding in this age group.

Clinical Context and Differential Diagnosis

This clinical presentation is highly suggestive of Meckel's diverticulum:

• Age: The 11-month-old age is classic for Meckel's diverticulum presentation, which typically manifests in children under 2 years 1
• Bleeding pattern: Bright red blood mixed with dark "currant jelly" stool suggests significant lower GI bleeding with ectopic gastric mucosa causing ulceration 1
• Hemodynamic compromise: Heart rate of 160/min and severe anemia (Hb 70 g/L) indicate substantial blood loss requiring urgent diagnosis 2
• Normal coagulation: Rules out coagulopathy as a contributing factor 2

Why Radioisotope Imaging (Meckel's Scan) is the Answer

Technetium-99m pertechnetate scintigraphy (Meckel's scan) specifically detects ectopic gastric mucosa, which is present in approximately 50% of symptomatic Meckel's diverticula 1. This imaging modality:

• Detects bleeding at rates as low as 0.1-0.5 mL/min, making it more sensitive than angiography 3
• Is non-invasive and does not require bowel preparation in an already compromised infant 1
• Has high specificity for Meckel's diverticulum in the pediatric population when positive 1

Why Other Options Are Less Appropriate

Abdominal Ultrasonography

• Limited utility for detecting Meckel's diverticulum unless there is associated intussusception 1
• Cannot identify ectopic gastric mucosa or active bleeding sources in the small bowel 1
• May be useful for other pediatric abdominal pathology but not the primary investigation for this presentation

Barium Enema

• Primarily evaluates the colon, not the small bowel where Meckel's diverticulum is located 3
• While therapeutic barium enema has been reported for colonic diverticular bleeding in adults, this is not applicable to pediatric Meckel's diverticulum 4, 5
• The "foul-smelling, dark brownish-black stool" suggests small bowel pathology rather than colonic source 6

Barium Meal

• Evaluates the upper GI tract (esophagus, stomach, duodenum) but has poor sensitivity for detecting Meckel's diverticulum 3
• Small bowel radiology is "rarely of use" unless Crohn's disease is suspected, which is uncommon at 11 months 3
• Does not provide therapeutic benefit and delays definitive diagnosis 3

Clinical Algorithm for This Patient

1. Immediate stabilization: Continue volume resuscitation with crystalloids and blood transfusion to maintain Hb >7 g/dL (target 7-9 g/dL) 2

2. Radioisotope imaging (Meckel's scan): Perform technetium-99m pertechnetate scintigraphy as the primary diagnostic test 1

3. If Meckel's scan is positive: Proceed to surgical consultation for definitive management (diverticulectomy or segmental resection) 1

4. If Meckel's scan is negative but bleeding persists: Consider CT angiography if the child becomes hemodynamically unstable, or colonoscopy after stabilization to evaluate for other causes 2, 7

Critical Pitfalls to Avoid

• Do not delay diagnosis with less specific imaging modalities in a hemodynamically compromised infant 2
• Do not assume colonic pathology based solely on bright red blood—in infants, Meckel's diverticulum commonly presents this way 1
• Do not perform colonoscopy first in this age group with this presentation, as the bleeding source is likely in the small bowel 3, 6
• Recognize that angiography requires active bleeding at ≥1 mL/min and has only 30-47% sensitivity, making it less ideal than nuclear medicine imaging for intermittent bleeding 7

The combination of age, bleeding pattern, and hemodynamic compromise makes Meckel's diverticulum the leading diagnosis, and radioisotope imaging is the most specific and sensitive non-invasive test to confirm this source 1.