Imaging recommendation · Abdomen · Pelvis

Lower GI bleed

Colonoscopy after bowel prep (no contrast).

NM — Tc-99m labeled RBC scan (iv contrast).

CT — CT Enterography or Capsule Endoscopy (iv contrast).

Recommended: CTA Abdomen / Pelvis (if active); colonoscopy is the preferred imaging study for lower gi bleed. CTA for ongoing bleed.

Recommended study

CTA Abdomen / Pelvis (if active); colonoscopy

CT IV contrast Preferred Abdomen · Pelvis EmergencyAcute inpatient Reviewed 2026-05

CTA for ongoing bleed. Tagged RBC scan for slow / intermittent. IR for embolization.

Stable patient with formed stool + minor bleed

Colonoscopy after bowel prep No contrast

Intermittent or slow bleed

NM Tc-99m labeled RBC scan IV contrast

Obscure source (negative EGD and colonoscopy)

CT CT Enterography or Capsule Endoscopy IV contrast

Massive lower GI bleed mimicking UGIB

Brisk upper source can present with hematochezia — rule out with NG aspirate or upfront EGD if unstable.

Young patient with painless hematochezia

Consider Meckel diverticulum — Tc-99m pertechnetate scan.

Diverticular and angiodysplasia bleeds together account for the majority of LGIB.
CT extravasation detection limit ~0.3 mL/min; nuclear scan ~0.1 mL/min but lower spatial localization.
Hemodynamic instability + hematochezia = mesenteric ischemia until proven otherwise.