CT for Evaluation of Acute Abdominal Pain is Less Accurate Without Contrast
Dr. Gordon
Clinical question: How does the addition of contrast to a CT abdomen and pelvis ordered to evaluate abdominal pain in an emergency department (ED) setting impact diagnostic accuracy?
Background: Although contrast-enhanced CT has historically been the imaging of choice to evaluate abdominal pain in the acute setting, concerns about complications from contrast use (e.g., risk of contrast-induced acute kidney injury) and contrast shortages can result in these scans being ordered without contrast. At this point, it is unclear to what degree withholding the contrast causes a diagnostic error; this is important to clarify in order to have better-informed decision making regarding the use of contrast in this patient population.
Study design: Retrospective study
Setting: Patients were from a single, quaternary care, academic ED; radiologists were from three centers
Synopsis: The study included 201 consecutive ED patients who were ≥18 years old and had a dual-energy contrast-enhanced CT (intravenous and oral) ordered for evaluation of acute abdominal pain. Using these CT scans, researchers digitally subtracted iodine to create virtual unenhanced CT data. Experienced radiologists performed a blinded review of the unenhanced CT scans, and these findings and recommendations were compared to the interpretations of the contrast-enhanced CT that served as the “reference standard.” For primary and important secondary diagnoses, unenhanced CT was approximately 30% less accurate than contrast-enhanced CT (both false positive and false negative). Hospitalists should factor in the reduced accuracy of unenhanced CT scans for acute abdominal pain, both in their decision making surrounding ordering these studies and in interpreting the results of imaging that was already obtained in the ED. Limitations include the universal use of oral contrast for the contrast-enhanced CT and the fact that it was always subtracted from the unenhanced CTs.
Bottom line: When working up acute undifferentiated abdominal pain, CT scans should be ordered contrast-enhanced as much as possible in order to improve diagnostic accuracy.
Citation: Shaish H, et al. Diagnostic accuracy of unenhanced computed tomography for evaluation of acute abdominal pain in the emergency department. JAMA Surg. 2023;158(7):e231112.
Dr. Gordon is the associate program director of Maine Medical Center’s internal medicine residency program, a hospital medicine attending at Maine Medical Center, Portland, Maine, and an assistant professor at Tufts University School of Medicine, Boston.