Clinical Conundrum — Lower GI Bleeding: Who Needs a CTA?

Written by Amar Bukvic DO
REBEL EM
Medical Category: Abdominal and Gastrointestinal
Active Bleeding, Anticoagulation, Colonoscopy, CT Angiography, CTA, Gastrointestinal Bleeding, Lower GI Bleeding, Oakland Score, Risk Stratification

May 18, 2026

👉 Bottom Line Up Top

CTA is the preferred initial diagnostic test in an unstable patient with a suspected active lower gastrointestinal bleeding (LGIB) but should not be routinely obtained in all patients.

🤕 Case

A 78-year-old man with a history of atrial fibrillation on apixaban, hypertension and diabetes presents with rectal bleeding. He states that last night (12 hours prior to presentation), he had a bowel movement with red blood covered stool as well as blood in the bowl. Initial vital signs are: HR 84 BP 151/78 RR 16 Temp 98.9 O2 sat 98% on RA. The exam is unremarkable. Rectal exam reveals no external hemorrhoids and brown stool with no active bleeding. Labs are unremarkable including a hemoglobin of 13.1 mg/dl. The patient had a normal colonoscopy 7 years prior. You speak to the patient’s primary doctor to arrange follow up and he asks if you think getting a CTA would be helpful.

🗣️ What Your Gut Says

GI will want me to order a CTA for every patient with a LGIB, may as well order it.

📈 What The Evidence Says

Acute LGIB can lead to significant mortality and morbidity if not diagnosed and treated appropriately. The estimated incidence of LGIB is approximately 20-27 people per 100,000 and has a 4-10% mortality rate (Adegboyega 2019).

The initial evaluation of a LGIB begins with a history and physical and determination of the stability of the patient (Ahmed 2012). After the initial assessment, CTA can be considered. The CTA is a triple-phase stud composed of an unenhanced CT of the abdomen, an arterial phase contrasted CT, and a venous phase contrasted CT (Baliyan 2019).

CTA offers a noninvasive, fast, and accurate way of detecting bleeding as low as 0.3 mL/min with a sensitivity and specificity of 90% and 92%, respectively (Chua 2008). CTA also offers additional information that can help guide management and alter therapies including signs of liver cirrhosis or portal hypertension.

The decision on which patient should get a CTA can be decided based on whether the bleeding is active or not. Active bleeding in the ED or any bleeding reported by the patient within 4 hours of arrival satisfies this condition as does abnormal vital signs such as hypotension, tachycardia, recent transfusion, or altered mental status (Sengupta 2023).

Patients without active bleeding in the ED or 4 hours prior and stable vital signs should not routinely get CTAs. Lack of clinically significant bleeding decreases the diagnostic yield of CTAs. The preferred diagnostic for these patients would be inpatient or outpatient colonoscopy as determined by gastroenterology or using the Oakland Score; a prognostic scoring system to determine safety of discharge in LGIB (EMRAP 2024).

Harmful effects of the CTA include increased radiation and potential adverse reactions to contrast (Expert Panel on Interventional Radiology 2021). It is also a resource-intense imaging modality that should be selectively used for LGIB as specified. Every LGIB does not benefit from a CTA.

Selective use of CTAs for LGIB as detailed in this post is agreed by both the American College of Radiology and Gastroenterology (Prasad 2021).

🚨 Clinical Bottom Line

Patients that are unstable, have an active bleed, or have had bleeding within 4 hours should get a CTA. The yield of routine CTAs without an active bleed is very low. For stable patients, admission for a colonoscopy is appropriate.

📚 References

Adegboyega T, Rivadeneira D. Lower GI Bleeding: An Update on Incidences and Causes. Clinics in colon and rectal surgery 2019; 33(1), 28–34. PMID:31915423
Ahmed A, Stanley AJ. Acute upper gastrointestinal bleeding in the elderly: aetiology, diagnosis and treatment. Drugs Aging. 2012;29(12):933-940. PMID: 23192436
Baliyan V et al. Vascular computed tomography angiography technique and indications. Cardiovasc Diagn Ther 2019; 9(Suppl 1), S14–S27. PMID: 31559151
Chua AE, Ridley LJ. Diagnostic accuracy of CT angiography in acute gastrointestinal bleeding. J Med Imaging Radiat Oncol. 2008;52(4):333-338. PMID: 18811756
Sengupta N et al. Management of Patients With Acute Lower Gastrointestinal Bleeding: An Updated ACG Guideline. Am J Gastroenterol. 2023;118(2):208-231. PMID: 36735555
Johnson W, Xian, L. “Lower GI Bleeding.” EM:RAP, 22 July 2024, www.emrap.org/episode/ep21/lowergibleeding. Accessed 1 Mar. 2026. https://www.emrap.org/episode/ep21/lowergibleeding
Expert Panel on Interventional Radiology ACR Appropriateness Criteria® Radiologic Management of Lower Gastrointestinal Tract Bleeding: 2021 Update. J Am Coll Radiol. 2021;18(5S):S139-S152. PMID: 33958109

Post Peer Reviewed By: Mark Ramzy, DO (X: @MRamzyDO), and Marco Propersi, DO (X: @Marco_Propersi)

Authors

Amar Bukvic, DO

PGY 3 Chief Emergency Medicine Resident

Staten Island University Hospital

Anand Swaminathan, MD, MPH

Associate Professor Emergency Medicine, Zucker School of Medicine

Staten Island University Hospital

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🔎 Your Deep-Dive Starts Here

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Cite this article as: Amar Bukvic DO, "Clinical Conundrum — Lower GI Bleeding: Who Needs a CTA?", REBEL EM blog, May 18, 2026. Available at: https://rebelem.com/clinical-conundrum-lower-gi-bleeding-who-needs-a-cta/.