Diagnostic Approaches for Gastrointestinal Bleeding

Primary Purpose and Mechanism

The American College of Radiology recommends tagged RBC scans to detect active bleeding by tracking radiolabeled red blood cells that leak from blood vessels into the GI lumen, with a sensitivity to detect bleeding rates as low as 0.05-0.2 mL/min 1, 2
Tagged RBC scans require ongoing active hemorrhage at the time of imaging to be positive, and imaging is performed dynamically over 1-24 hours to capture intermittent bleeding episodes 1
The Radiology society identifies ectopic gastric mucosa within a Meckel's diverticulum using Tc-99m pertechnetate scintigraphy, which accumulates in gastric mucosa, creating a fixed focal area of uptake 3

The American College of Radiology suggests that tagged RBC scans are useful for active GI bleeding of unknown location, and for intermittent or slow-rate bleeding that may be missed by angiography or CTA 1
The Radiology society recommends Meckel's scans for young patients with unexplained lower GI bleeding after negative upper endoscopy and colonoscopy, with the highest diagnostic accuracy when the patient has GI bleeding with anemia 3

The American College of Radiology notes that tagged RBC scans have a high sensitivity for detecting bleeding, but a poor positive predictive value for precise localization, with variable diagnostic efficacy and poor localization accuracy 1, 4, 2
The Radiology society reports that Meckel's scans have a sensitivity of 89% and specificity of 98% for detecting symptomatic Meckel's diverticulum, with positive and negative predictive values approaching 100% in anemic patients with GI bleeding 3

For acute active bleeding, the American College of Radiology recommends proceeding directly to CTA for hemodynamically unstable or high-risk patients, and considering tagged RBC scans for hemodynamically stable patients with intermittent bleeding 4, 2, 1
For unexplained GI bleeding after negative endoscopy, the Radiology society suggests that Meckel's scan is the diagnostic test of choice for young patients with painless rectal bleeding and anemia, while CT enterography may be used for older patients or atypical presentations 3, 2

Painless rectal bleeding is a classic presentation of Meckel's diverticulum, particularly in younger patients, and a radionuclide Meckel scan using 99mTc pertechnetate is the diagnostic test of choice for suspected bleeding from Meckel's diverticulum, as it detects ectopic gastric mucosa 5, 6
Most symptomatic Meckel diverticula with bleeding are found in children and young adults 5
Obstruction can occur due to volvulus around a fibrous band connecting the diverticulum to the umbilicus or entrapment of small bowel beneath a mesodiverticular band 7

CT scan of abdomen and pelvis with contrast is highly accurate for diagnosing complications like diverticulitis or perforation 7
Meckel scan (99mTc pertechnetate scintigraphy) is appropriate in young patients with unexplained lower gastrointestinal bleeding 5, 8
Negative upper GI endoscopy and colonoscopy in a patient with GI bleeding should prompt consideration of Meckel's diverticulum as a source 8, 9

The American College of Radiology notes that Meckel's diverticulum contains all intestinal wall layers, including muscularis propria 10
CT enterography can help identify Meckel's diverticulum and exclude other etiologies, as recommended by the American College of Radiology 10

CT enterography can help identify Meckel's diverticulum when bleeding is not active, as recommended by the American College of Radiology 11, 12