In a 60‑year‑old woman with impaired renal function presenting with brisk bright‑red, clot‑filled stools and hemodynamic compromise, and a normal upper gastrointestinal tract, what is the most likely source of bleeding and what is the next diagnostic and therapeutic step?

CT Angiography (CTA) is the next step for this hemodynamically unstable patient with bright red rectal bleeding and a normal upper GI tract.

In a 60-year-old woman with hemodynamic compromise, brisk bright-red bleeding per rectum, impaired renal function, and a confirmed normal upper GI tract, proceed immediately to CT angiography to localize the bleeding source before planning endoscopic or radiological therapy. 1

Rationale for CTA as First-Line Investigation

The British Society of Gastroenterology 2019 guidelines provide a strong recommendation that CTA should be the first-line investigation in patients with active lower GI bleeding and a shock index ≥1 (heart rate/systolic BP >1) 1. This patient's hemodynamic compromise places her in this high-risk category.

Why CTA Over Colonoscopy in This Scenario:

• Rapid accessibility with sensitivity of 79-95% and specificity of 95-100% for active bleeding 1
• No bowel preparation required – critical when the patient is unstable
• Can detect bleeding at rates as low as 0.3-1.0 mL/min 1
• Localizes bleeding throughout the entire GI tract including small bowel, which colonoscopy cannot assess 1
• Higher diagnostic yield in hemodynamically unstable patients 1

Critical Caveat: Renal Impairment

This patient has impaired renal function, which creates a significant challenge. Follow Royal College of Radiologists guidelines for contrast administration in renal impairment 1. The decision requires weighing:

• Risk of contrast-induced nephropathy versus
• Risk of mortality from uncontrolled hemorrhage

In hemodynamically unstable bleeding, the mortality risk typically outweighs nephrotoxicity concerns, but this requires senior clinical discussion and informed consent when possible.

Alternative if CTA Contraindicated:

If contrast is absolutely contraindicated, proceed directly to mesenteric angiography with potential for therapeutic embolization 2. The ACR 2021 guidelines support transcatheter arteriography/embolization as an equivalent alternative to CTA in hemodynamically unstable patients 2.

Most Likely Bleeding Sources

Given the clinical presentation:

1. Lower GI tract sources (colon/rectum) – most probable given bright red blood

2. Small bowel angiodysplasia – particularly relevant given her renal impairment 3, 4, 5

   • Small bowel angiodysplasia occurs with increased frequency in chronic renal failure patients
   • Can cause severe bleeding requiring transfusion
   • Often multiple lesions in 40-75% of cases 4

3. Diverticular bleeding – common cause of massive lower GI bleeding in this age group

Subsequent Management Algorithm

If CTA Identifies Bleeding Source:

• Active extravasation visualized → Proceed to transcatheter embolization for immediate hemostasis 2
• Lesion identified but no active extravasation → Colonoscopy once hemodynamically stable with adequate bowel preparation 1

If CTA is Negative:

• Patient remains unstable → Consider mesenteric angiography if bleeding rate may be intermittent 1
• Patient stabilizes → Colonoscopy within 24 hours after bowel preparation 6
• Recurrent bleeding with negative initial workup → Video capsule endoscopy for small bowel evaluation, particularly given renal impairment increasing angiodysplasia risk 1, 5

Key Pitfalls to Avoid

• Do NOT place a nasogastric tube – it does not reliably aid diagnosis, does not affect outcomes, and causes complications in one-third of patients 1
• Do NOT delay imaging for bowel preparation in unstable patients 1
• Do NOT perform urgent colonoscopy in hemodynamically unstable patients – no advantage over elective timing and risks inadequate visualization 1
• Do NOT repeat CTA within 24 hours unless bleeding becomes more brisk – mesenteric angiograms done within 24 hours of negative CTA have zero positive yield 1

Therapeutic Considerations

Once the source is localized:

• Endoscopic therapy (mechanical clips, thermal coagulation, injection) for accessible colonic lesions 6
• Transcatheter embolization for ongoing hemorrhage or inaccessible lesions 2
• Surgery reserved for failed endoscopic/radiologic intervention or when these are unavailable 2

The elevated BUN/creatinine ratio in this patient with renal impairment may confound traditional markers suggesting upper GI bleeding 1, but since upper endoscopy was normal, focus remains on lower GI and small bowel sources.