For a patient with an acute gastrointestinal bleed that cannot be evaluated by endoscopy, what contrast‑enhanced CT abdomen and pelvis protocol should be used?

CT Imaging Protocol for Acute GI Bleeding When Endoscopy Cannot Be Performed

For a patient with acute gastrointestinal bleeding that cannot be evaluated by endoscopy, order CT angiography (CTA) of the abdomen and pelvis WITHOUT and WITH IV contrast using a multiphasic protocol—never order standard "CT abdomen with contrast." 1, 2

Critical Protocol Requirements

The Correct Order is CTA, Not Standard CT

• CTA is a distinct procedure from standard CT with IV contrast—the ACR explicitly states there is no significant literature supporting standard CT abdomen/pelvis with IV contrast for GI bleeding evaluation 1, 3
• Standard CT with contrast is rated as "usually not appropriate" (rating 2-3) for GI bleeding across all clinical scenarios 3
• CTA requires specific arterial-phase timing and multiphasic acquisition that standard CT protocols do not provide 2, 3

Multiphasic Acquisition Protocol

• The optimal protocol includes three phases: unenhanced + arterial + portal venous phase, achieving 92% sensitivity 1
• This is superior to protocols using only arterial or portal venous phase alone (83% sensitivity) 1
• The ACR recommends noncontrast images with 100% consensus for single-energy CT 1, 2

Why Each Phase Matters

• Unenhanced phase: Identifies baseline high-attenuation material (sentinel clot) that could be mistaken for active bleeding on contrast-enhanced images 1, 2
• Arterial phase: Detects active arterial extravasation with sensitivity down to 0.3 mL/min bleeding rate 2, 3
• Portal venous/delayed phase (70-90 seconds after contrast bolus): Captures slower or intermittent bleeding not visible on arterial phase alone 1

Anatomic Coverage

Image Both Abdomen AND Pelvis

• Both regions must be included because the bleeding site is unclear without prior endoscopy 1, 2
• Imaging abdomen alone has no significant literature support 1
• Do not include chest unless there is specific concern for esophageal bleeding 1

Critical Technical Details

Oral Contrast Must Be Avoided

• Never give positive oral contrast—it renders the examination nondiagnostic by obscuring intraluminal hemorrhage 1, 3
• Oral water can dilute intraluminal hemorrhage and should also be avoided 1

Additional Technical Requirements

• Thin collimation (≤1 mm) enables high-quality multiplanar reformations necessary for precise localization 2, 3
• 3D reconstructions are required elements of CTA 3

Diagnostic Performance

Accuracy Metrics

• Meta-analysis of 22 studies (672 patients) demonstrates CTA sensitivity of 85% and specificity of 92% for active GI bleeding 1
• Positive predictive value: 86%; negative predictive value: 92% 3
• Can detect bleeding rates as slow as 0.3 mL/min, more sensitive than conventional angiography 2, 3

Clinical Utility

• CTA leads to faster triage toward definitive treatment compared to endoscopy or nuclear medicine studies 1, 2
• Greater contrast extravasation volume correlates with need for hemostatic therapy, intraprocedural active bleeding, and massive transfusion 1
• If CTA identifies active bleeding, it provides a roadmap for subsequent catheter angiography with technical success rates up to 95% 3

Common Pitfalls to Avoid

Ordering Errors

• Do not order "CT abdomen and pelvis with IV contrast"—this is standard CT, not CTA 1, 3
• Do not order CTA of abdomen only without pelvis 1
• Do not order single-phase protocols (arterial or portal venous alone) 1

Technical Pitfalls

• Intermittent bleeding may result in false-negative studies if patient is not actively bleeding during scan acquisition 3, 4
• Virtual noncontrast images from dual-energy CT can substitute true noncontrast scans, but this remains site-specific and not universally accepted 1, 5

Alternative Modalities (When CTA is Not Appropriate)

When to Consider Visceral Arteriography Instead

• Visceral arteriography is rated equally appropriate (rating 8-9) when endoscopy confirms bleeding but treatment is not possible or bleeding continues after endoscopic treatment 1, 3
• Arteriography allows simultaneous diagnosis and therapeutic embolization 1, 3
• Success rate of 88-100% for diagnosis of endoscopically refractory bleeding 1

Nuclear Medicine Has Limited Role

• Tc-99m-labeled RBC scanning has no significant literature support for initial imaging of suspected GI bleeding without endoscopy 1
• CTA is superior to nuclear medicine for faster triage to definitive treatment 1

What NOT to Order

• Fluoroscopy upper GI series with barium or iodine has no role in acute GI bleeding 1
• MR enterography has no significant literature support for acute overt GI bleeding 1