What is the preferred contrast route for a CT abdomen in patients with active Gastrointestinal (GI) bleeding, Intravenous (IV) or oral?

CT Abdomen for Active GI Bleeding: IV Contrast Only (No Oral Contrast)

For patients with active GI bleeding, CT angiography (CTA) of the abdomen and pelvis should be performed WITHOUT and WITH IV contrast (multiphasic protocol), and oral contrast should NOT be administered. 1

Why Oral Contrast is Contraindicated

• Oral contrast renders the examination nondiagnostic for active bleeding because positive oral contrast material obscures intraluminal blood and contrast extravasation 1
• Oral water can dilute intraluminal hemorrhage, making detection of bleeding impossible 1
• CT enterography, which requires large volumes of oral contrast (900-1200 mL), is specifically NOT useful for detecting acute active bleeding due to this dilution effect 2

The Optimal Protocol: Multiphasic CTA Without and With IV Contrast

• Multiphasic CTA (unenhanced + arterial + portal venous phase) achieves 92% sensitivity for detecting GI bleeding, compared to only 83% for protocols using only arterial or portal venous phase alone 1
• The American College of Radiology recommends noncontrast images with 100% consensus for CTA performed on single-energy CT 1
• Noncontrast images are essential for identifying sentinel clot and distinguishing inherently hyperdense intraluminal material from contrast extravasation 1

Why Both Phases Matter

• Unenhanced phase: Identifies baseline high-attenuation material (sentinel clot) that could be mistaken for active bleeding on contrast-enhanced images 1
• Arterial phase: Detects active arterial extravasation with sensitivity down to 0.3 mL/min bleeding rate 1
• Portal venous/delayed phase: Captures slower or intermittent bleeding that may not be visible on arterial phase alone 1

Imaging Both Abdomen AND Pelvis

• Both abdomen and pelvis should be imaged because the bleeding site is typically unclear without prior endoscopy 1
• The American College of Radiology states there is no significant literature supporting imaging of abdomen alone for GI bleeding 1

Common Pitfall to Avoid

• Do not order standard "CT abdomen with IV contrast" - this is distinct from CTA and lacks the multiphasic arterial timing necessary to detect active bleeding 1
• CTA is a separate, specific procedure with different technical parameters than routine contrast-enhanced CT 1

Clinical Performance

• Meta-analysis of 22 studies (672 patients) demonstrates CTA sensitivity of 85% and specificity of 92% for active GI bleeding 1
• CTA leads to faster triage toward definitive treatment compared to endoscopy or nuclear medicine studies 1