IS Case 91: GI Bleed at Descending Colon

Chandler Shyu, MD, MPH

Imaging Sciences URMC 2008
Publication Date: 2009-05-20


Patient is an elderly female with bright red blood per rectum. Tagged RBC scan requested to locate site of bleed.


Serial planar images of the abdomen demonstrate accumulation of radiotracer at the descending colon (40 minutes image). Subsequently, the radiotracer is seen passing into sigmoid and colon.


GI Bleed at descending colon


Tagged RBC scan is commonly used as the first line exam to localize GI bleed prior to interventions such as colonoscopy or angiography. It offers several advantages including better sensitivity and a longer examination window compared to other modalities.

Tagged RBC scan can detect bleed at rate of 0.1cc/min compared to 1cc/min for angiography. Due to the intermittent nature of GI bleeds, other modalities are prone to false negative if there is no active, detectable extravasation at the time of scope or angiography. RBC-labeled with 99TC on the other hand allows imaging up to 24 hours after intravenous injection.

The best diagnostic clue for positive GI bleed is radiotracer accumulation in a tubular structure which moves over time. Common pitfalls to avoid include recognizing normal tracer accumulation in organ and blood vessels and poor 99Tc labeling which may result in false GI luminal activity.


  1. Morton KA, Clark PB, Blodgett TM, et al. Diagnostic Imaging: Nuclear Medicine. Amirsys 2007. Section 8, pgs 126-129.

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