Timothy L. Haaga MD, Presenter: Nothing to Disclose

Sun Ho Ahn MD, Abstract Co-Author: Nothing to Disclose

Gregory Joseph Dubel MD, Abstract Co-Author: Nothing to Disclose

Don C. Yoo MD, Abstract Co-Author: Nothing to Disclose

Richard B. Noto MD, Abstract Co-Author: Stockholder, General Electric Company Consultant, Molecular Insight Pharmaceuticals, Inc

Tc99m-labelled red blood cell (Tc99m RBC) scans detect bleeding at a rate of roughly 0.1 mL/h, approximately ten times slower than that detectable with conventional angiography. The primary purpose of this study is to evaluate how the intensity of a bleeding focus on Tc99m RBC scanning relates to the likelihood of positive findings on conventional angiography.

A retrospective review was conducted on PACS of all Tc99m RBC scans performed from 2003 through July 2011, and all visceral angiograms performed following Tc99m RBC scans during the same time period. Tc99m RBC scans initially interpreted as positive were reviewed independently by two board-certified, nuclear medicine (NM) fellowship-trained radiologists who were blinded to the initial interpretation. An RBC scan was considered 'intensely positive' by NM readers if intensity of the bleeding focus exceeded that of aortic blood pool and liver. Two board-certified, fellowship-trained interventional radiologists (IR), blinded to any interpretation of the Tc99m RBC scans, independently reviewed visceral angiograms.  An angiogram was considered positive if it demonstrated extravasation or an etiology for bleeding.

174 Tc99m RBC scans and 112 visceral angiograms were reviewed. Of the 112 patients who proceeded to angiogram following RBC scan, 60 and 47 RBC scans were read as intensely positive by NM readers A and B, respectively. 21/112 angiograms were read as positive by one or both IR readers.  Of 21 patients with positive angiograms, the preceding RBC scans were read as intensely positive in 19/21 cases for reader A and 15/21 cases for reader B. Sensitivity, specificity, PPV and NPV of an intensely positive RBC scan for a positive angiogram were thus 91%,55%, 32% and 91%, respectively, for reader A and 71%, 65%, 32% and 96%, respectively, for reader B. 

Intensity of a bleeding focus on Tc99m RBC scan greater than that of aorta and liver has a high negative predictive value for a positive angiogram. If a bleeding focus demonstrates equal or lesser activity than that of liver or aorta on Tc99m RBC scan there is thus a high likelihood of a negative subsequent conventional angiogram.

By clarifying patients' pre-test probability of positive angiography, grading of bleeding intensity on RBC scan has the potential to lessen the number of unnecessary visceral angiograms performed.

Haaga, T, Ahn, S, Dubel, G, Yoo, D, Noto, R, Bleeding Focus on Tc 99m Red Blood Cell (RBC) Scintigraphy in Acute Lower Gastrointestinal Bleeding (LGIB): Relationship between Intensity of Bleeding Focus and Positive Rate of Subsequent Conventional Angiography.  Radiological Society of North America 2013 Scientific Assembly and Annual Meeting, December 1 - December 6, 2013 ,Chicago IL. http://archive.rsna.org/2013/13019010.html