Correlation of CT Angiography and 99mTechnetium-Labeled Red Blood Cell Scintigraphy to Catheter Angiography for Lower Gastrointestinal Bleeding: A Single-Institution Experience

Clinical Question
Can greater adoption of CT angiography or 99mTechnetium-labeled red blood cell (RBC) scintigraphy reduce the number of nontherapeutic catheter angiography (CA) in the management of lower gastrointestinal bleeding (LGIB)?

Take-away Point
Greater adoption of CT angiography rather than RBC scintigraphy may reduce the number of nontherapeutic CAs given CT’s greater positive correlation to CA and non-increased nephrotoxicity.

Reference
Correlation of CT Angiography and 99mTechnetium-Labeled Red Blood Cell Scintigraphy to Catheter Angiography for Lower Gastrointestinal Bleeding: A Single-Institution Experience. Speir, E. J. et al. Journal of Vascular and Interventional Radiology (JVIR), Volume 30, Issue 11, 1725-1732.

Study design
Single-institution, retrospective study of 223 CAs with either pre-procedural CT angiography, RBC scintigraphy, or both for LGIB with laboratory creatinine review 48-72 hours after CA.

Funding Source
No reported funding

Setting
Academic hospital, Emory University Hospital, United States of America.







Figure 2.  Positive predictive values of CT angiography (CTA) compared to RBC scintigraphy (NM for nuclear medicine) overall, across clinical variants of LGIB, overall excluding Variant 4 LGIB, and studies completed within 4 hours of CA.

Summary

99mTechnetium-labeled red blood cell (RBC) scintigraphy has traditionally served as the initial diagnostic study for imaging evaluation of lower gastrointestinal bleeding (LGIB) given its superior sensitivity. However, frequent subsequent non-therapeutic catheter-based intervention following positive RBC scintigraphy and the advances of CT angiography with superior localization capability have led to the proposal of incorporating CT angiography into the standard management of LGIB. Nonetheless, there was a paucity of literature on the comparative correlations between the two modalities to subsequent catheter angiography. Effects of additional contrast dose on renal function with CT angiography prior to catheter angiography also remained unclear.

The authors performed a retrospective, single institution (3 practicing hospitals) of 223 cases (unique patient count of 207) of catheter angiography for evaluation of LGIB with pre-procedural CT angiography, RBC scintigraphy, or both. Catheter angiography was used as the reference standard. All 4 variants of LGIB were included and were used for sub-analysis. Exclusion criteria included no CT angiography or RBC scintigraphy within 30 hours of catheter angiography, prophylactic embolization, provocative catheter angiography, and inadequate pre-procedural imaging or procedural evaluation.

Out of the 223 cases of catheter angiography, 38 had CT angiography, 173 had RBC scintigraphy, and 12 had both types of pre-procedural imaging. The authors found CT angiography had a higher positive correlation of 67.7% with catheter angiography, compared to 29.3% of RBC scintigraphy. This difference was more dramatic if the pre-procedural imaging were completed within 4 hours preceding catheter angiography. Interestingly, positive correlation of RBC scintigraphy with catheter angiography was reported to be 75.0% when performed within 1 hour of catheter angiography. No significant dose-toxicity relationship between contrast and renal function was found. No significant differences of CIN incidence was found between the two arms.

Commentary

The authors in this study have demonstrated greater positive correlation of CT angiography with catheter angiography compared to RBC scintigraphy for assessing LGIB. Furthermore, they have showed non-increased nephrotoxicity associated with the additional contrast dose when CT angiography was utilized prior to catheter angiography. This study, with its retrospective nature and unequal CT angiography versus RBC scintigraphy case proportions, had its inherent limitations. Clinicians and proceduralists would have skewed towards proceeding with catheter angiography or not given the known high negative predictive value of CT angiography and high sensitivity of RBC scintigraphy. Therefore, future prospective randomized clinical trials may be necessary to definitely answer the question. The timing aspect, however, should not be understated. Dramatically increased positive correlations to catheter angiography were observed with shorter positive pre-procedural imaging to catheter angiography time regardless of the imaging choice. This highlighted the importance of prompt transitioning from pre-procedural imaging to catheter-based intervention which should be an important focus of a standardized LGIB management protocol.

Post Author
Ningcheng (Peter) Li, MD, MS
Integrated Interventional Radiology Resident, PGY-3
Department of Interventional Radiology
Oregon Health and Science University, Dotter Interventional Institute

@NingchengLi