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Online supplemental material is available for this article. See also the editorial by Grant in this issue.

Purpose: To investigate the correlation of computed tomography (CT) angiography and 99mTechnetium-labeled red blood cell (RBC) scintigraphy to catheter angiography (CA) in the management of lower gastrointestinal bleeding (LGIB) while considering potential nephrotoxic effects of iodinated contrast.Materials and Methods: From November 2012 to August 2017, 223 CAs performed for LGIB, including massive, ongoing, and obscure bleeding, were retrospectively identified in patients with pre-procedural CT angiography or RBC scintigraphy. Positive correlations and sensitivities were calculated for CT angiography and RBC scintigraphy using CA results as reference. Correlations were then compared while considering certain clinical presentations of LGIB. Contrast dose was compared with maximum creatinine recorded 48-72 hours after.Results: Thirty-eight patients underwent CT angiography; 173 patients underwent RBC scintigraphy; and 12 patients completed both studies. CT angiography had a positive correlation of 67.7% (95% confidence interval [CI]: 57.0, 76.7) and sensitivity of 85.2% (95% CI: 66.3, 95.8), whereas RBC scintigraphy had a positive correlation of 29.3% (95% CI: 27.7, 31.0) and sensitivity of 94.4% (95% CI: 84.6, 98.8). CT angiography had higher positive correlation across all clinical presentations. No dose-toxicity relationship was observed between contrast and renal function (R2: 0.008), nor was there a difference in incidence of contrast-induced nephropathy between CT angiography and RBC scintigraphy (P = .30).Conclusions: CT angiography has greater positive correlation to CA than RBC scintigraphy for assessing LGIB in active stable as well as hemodynamically unstable LGIB. As such, greater adoption of CT angiography may reduce the number of nontherapeutic CAs performed. Additional contrast associated with CT angiography does not result in increased nephrotoxicity. [ABSTRACT FROM AUTHOR]