What is the best initial CT (Computed Tomography) abdomen study to assess for a Gastrointestinal (GI) bleed?

From the Guidelines

The best initial CT abdomen study to assess for a gastrointestinal (GI) bleed is a multiphasic CT angiography (CTA) that includes non-contrast, arterial, and portal venous phases. This examination is preferred because it can detect bleeding rates as low as 0.3-0.5 mL/minute, provides excellent anatomic detail to localize the bleeding source, and helps differentiate between arterial and venous sources of hemorrhage 1. The protocol typically involves administering 100-150 mL of iodinated contrast material at a rate of 4-5 mL/second, with arterial phase imaging beginning approximately 25-30 seconds after contrast injection and portal venous phase at 60-70 seconds.

Key Considerations for CTA Protocol

• Non-contrast phase is useful for detecting intraluminal high-attenuation material that may mimic intraluminal blood on contrast-enhanced images 1.
• Arterial phase is crucial for detecting active arterial bleeding.
• Portal venous phase helps identify slower bleeding sources and provides better visualization of bowel wall abnormalities that might be causing the bleed.
• Oral contrast should not be given as it can render the examination nondiagnostic, and oral water can dilute intraluminal hemorrhage 1.

Evidence Supporting CTA

• A meta-analysis of 22 studies evaluating the accuracy of CTA for the diagnosis of active GI bleeding found that CTA had a sensitivity and specificity of 85% and 92%, respectively 1.
• CTA can detect bleeding rates as slow as 0.3 mL/min, which is comparable to or better than other imaging modalities such as conventional angiography and Tc-99m–labeled RBC scintigraphy 1.
• The use of CTA as the first test leads to faster triage of patients toward definitive treatment by angiography or endoscopy 1.

Clinical Implications

• CTA is a valuable tool in the assessment of GI bleeding, especially in cases where endoscopy is unsuccessful in localizing the bleeding source.
• The results of CTA can guide further management, including the decision to proceed with angiography, endoscopy, or surgery.
• A negative CTA result can help identify patients who may not require immediate intervention and can be managed conservatively 1.

From the FDA Drug Label

OMNIPAQUE diluted to concentrations from 6 mg Iodine/mL to 9 mg Iodine/mL administered orally in conjunction with OMNIPAQUE 300 at a concentration of 300 mg Iodine/mL administered intravenously are indicated in adults for use in contrast enhanced computed tomography of the abdomen Dilute oral plus intravenous OMNIPAQUE may be useful when unenhanced imaging does not provide sufficient delineation between normal loops of the bowel and adjacent organs or areas of suspected pathology.

The best initial CT abdomen study to assess for a GI bleed is a contrast-enhanced CT using oral and intravenous OMNIPAQUE. The recommended oral dosage is 500 mL to 1000 mL of OMNIPAQUE diluted to concentrations of 6 mg Iodine/mL to 9 mg Iodine/mL, administered about 20 to 40 minutes prior to the intravenous dose and image acquisition. The recommended intravenous dosage is 100 mL to 150 mL of OMNIPAQUE 300 2.

From the Research

Initial CT Abdomen Study for GI Bleed Assessment

The best initial CT abdomen study to assess for a GI bleed can vary depending on the specific circumstances of the patient. However, based on the available evidence, the following options can be considered:

• CT Angiography (CTA): CTA is a promising initial test for acute GI bleeding as it is universally available, can be performed rapidly, and may provide diagnostic information to guide management 3.
• Enhanced CT: Enhanced helical CT can be useful for the detection of an active lower GI bleeding source, and the procedure is brief, less invasive, and less demanding 4.
• Unenhanced CT: Unenhanced CT can be used to detect hemorrhage in the abdomen and pelvis, and it can determine the presence or absence of hemorrhage rapidly, as well as evaluate the amount and precise location of hemorrhage 5.
• CT Enteroclysis: CT enteroclysis can be used to evaluate patients with obscure GI bleeding, especially when the source of the bleeding cannot be detected by upper GI endoscopy and colonoscopy 6.
• CT Enterography: CT enterography can aid in identifying the location and cause of bleeding, and it is an important complementary tool to endoscopy, nuclear medicine, and angiography in evaluating patients with GI bleeding 7.

Key Considerations

When choosing the best initial CT abdomen study for GI bleed assessment, the following factors should be considered:

• The severity and location of the bleeding
• The patient's medical history and risk factors
• The availability and expertise of the imaging modalities
• The need for rapid diagnosis and treatment

Imaging Techniques

The optimal CT imaging technique for GI bleeding assessment may involve:

• Arterial and venous phases: Imaging in both phases can help identify the source of bleeding and evaluate the extent of hemorrhage 6.
• Intravenous contrast: The use of intravenous contrast can enhance the detection of bleeding and improve the diagnostic accuracy of CT scans 4, 6.
• Neutral enteral contrast: The use of neutral enteral contrast, such as methylcellulose, can help distend the small intestine and improve the visualization of the bowel 6.